Why does this Curtiss Kittyhawk have a Question Mark in its squadron code? Examples. Making statements based on opinion; back them up with references or personal experience. Convert a 0 V / 3.3 V trigger signal into a 0 V / 5V trigger signal (TTL). Similarly, is there a better way to return a list of all values for a given key than using a foreach? You may also use the IEnumerable.Select to only select a fewer properties as well from an object, which will cause the creation of an anonymous type. But doesn't this enumerate and sort the whole list? What is the best way to visualise such data? 2) If I can tell that it is an IList, use drzaus' approach, with a twist. How do I get the number of elements in a list (length of a list) in Python? Only get enough item in the list, but not get randomly. More info about Internet Explorer and Microsoft Edge. What to do to align text with chemfig molecules? i dont need this for anything in particular, im just trying out a bunch of things. How to get first N elements of a list in C#? - Stack Overflow (2) If K is close to N, then you will thrash a lot searching for an unclaimed index in your loop, causing the code to require an unpredictable amount of time. How can I get the data of specific property of the list instead of the objects? I convert it to a List through the following method: But I want the returned list to contain only the first property, lessonid, not all the Lesson properties. You may also use the IEnumerable.Select to only select a fewer properties as well from an object, which will cause the creation of an anonymous type. I created an extension for any generic collection. Although SelectMany works similarly to Select, it differs in that the transform function returns a collection that is then expanded by SelectMany before it is returned. Can I knock myself prone? @Jonah: I think so. The value of the first integer in the sequence. Convert from List into IEnumerable format. Where I use it, that does not matter though. This should be pretty fast, as it has nothing to check. What are the implications of constexpr floating-point math? I would use ILookup in your case. why? Why is this? SUBMIT GET UP TO $15* BACK VIA REBATE ON THE PURCHASE OF BUDWEISER, BUD LIGHT, BUDWEISER SELECT, OR BUDWEISER SELECT 55. How do they capture these images where the ground and background blend together seamlessly? Thanks for contributing an answer to Stack Overflow! Thanks for contributing an answer to Stack Overflow! And then, how about returning a list of keys for a given value? I hastily read it at first, and mistakenly thought you were indicating to sequentially choose each element with fixed probability k/n, which would have been wrong - but your adaptive approach appears correct to me. Kyle's algorithm required no alteration. var firstFiveArrivals = myList.Where ( [EXPRESSION]).Take (5).OrderBy ( [ORDER EXPR]); It will be faster than orderBy variant, because LINQ engine will not scan trough all list due to delayed execution, and will not . If K >= N/2, choose the indices which should NOT be kept, instead of the ones that should be kept. Does this change how I list it on my CV? Any recommendation? In Visual Basic query expression syntax, an Aggregate Into Count() clause translates to an invocation of Count. Here is a benchmark of three different methods: The testing will consist of benchmarking the performance with multiple different list sizes and selection sizes. Some information relates to prerelease product that may be substantially modified before its released. Remarks. However, its simple logic is inefficient when select/needed is close to the listSize with extended running time because of multiple retries to catch the last elements, as Paul was also mentioning in 2015 and as the benchmark with 50 among 50 confirms. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. The random in the hole list may not. Select is a projection or a conversion for each item. do note that the ticked answer is hopelessly wrong. Sorted by: 35. How can I get a random number of element from list, c# Select N elements from list uniformly without shuffle, Pick random element from list with probability, Lottery Analysis (Python Crash Course, exercise 9-15), Draw the initial positions of Mlkky pins in ASCII art, tmux session must exit correctly on clicking close button, Can the type 3 SS be obtained using the ANOVA function or an adaptation that is readily available in Mathematica. Find centralized, trusted content and collaborate around the technologies you use most. If you keep s sorted and track which contiguous intervals it has, you can implement it in O(k log k), but it's more work. c# - Getting all elements from an IEnumerable - Stack Overflow To learn more, see our tips on writing great answers. How can I add an item to a IEnumerable<T> collection? Using LINQ, how do I choose items at particular indexes? Could it be that you interchanged source and exceptions in your initial example? C# IEnumerable Examples - Dot Net Perls Program where I earned my Master's is changing its name in 2023-2024. Generates a sequence of integral numbers within a specified range. How to maximize the monthly 1:1 meeting with my boss? the benchmark suggests the "Random_RandomIdices" to be the best compromise. In the final act, how to drop clues without causing players to feel "cheated" they didn't find them sooner? If you cast a spell with Still and Silent metamagic, can you do so while wildshaped without natural spell? C# choosing random strings to be displayed, Unity: getting a maximum of 10 out of 20 questions quiz game Multiple Choice, Select k random elements from a list whose elements have weights, Pick N distinct items at random from sequence of unknown length, in only one iteration. I combined several of the above answers to create a Lazily-evaluated extension method. Find centralized, trusted content and collaborate around the technologies you use most. How do I make a flat list out of a list of lists? This method is implemented by using deferred . By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Are MSO formulae expressible as existential SO formulae over arbitrary structures? It is not Order object either. I saw larger LINQ queries which were way easier to read. How do I split a list into equally-sized chunks? Why a kite flying at 1000 feet in "figure-of-eight loops" serves to "multiply the pulling effect of the airflow" on the ship to which it is attached? If you want to convert to the non-generic one: Thanks for contributing an answer to Stack Overflow! What is the best way to visualise such data? Asking for help, clarification, or responding to other answers. Does this change how I list it on my CV? until you have k distinct elements in s. This has worst-case running time O(k^2). aAll questions were loaded in the a QuestionSorter list, which was then sorted using the List's Sort function and the first k elements where selected. How could the Intel 4004 address 640 bytes if it was only 4-bit? This allows you to do a foreach on it without explicitly having to check for null. What is the best way to visualise such data? The following uses Enumerable.Cast method to convert IEnumerable to a generic List. Given a list of length n select k random elements using C#. Take returns the first elements of an IEnumerable. Enumerable.Sum Method (System.Linq) | Microsoft Learn By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. But i get it now, thank you. I want to convert from IEnumerable to List. Looks simple but makes easiest way to convert. Why did Kirk decide to maroon Khan and his people instead of turning them over to Starfleet? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Definition Namespace: System. Asking for help, clarification, or responding to other answers. This method is implemented by using deferred execution. Should I sell stocks that are performing well or poorly first? Find centralized, trusted content and collaborate around the technologies you use most. In the final act, how to drop clues without causing players to feel "cheated" they didn't find them sooner? I think you are looking for Where instead of Select. How to resolve the ambiguity in the Boy or Girl paradox? My extension method first checks to see if the enumeration is null and if so creates an empty list. You can select the value you want first, like this: If you want to get the the specific row value from list using linq use the following code: Thanks for contributing an answer to Stack Overflow! or { 1, 2, 4 } depending on the flag set. What are the implications of constexpr floating-point math? (NOTE: there are multiple values for the key "qwer" and multiple keys for the value "asdf".). How do I clone a list so that it doesn't change unexpectedly after assignment? C#: IEnumerable, yield return, and lazy evaluation This however means, that now i can't return the ListOfStrings anymore. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Hence the second Enumerable is added to the set and duplicates are removed when the first Enumerable is added. Connect and share knowledge within a single location that is structured and easy to search. Does "discord" mean disagreement as the name of an application for online conversation? rev2023.7.5.43524. It has a period of 2^128-1 which is better than many RNGs.). @uckelman the question says nothing at all about that. What are the advantages and disadvantages of making types as a first class value? Is there an easier way to generate a multiplication table? 6 Answers. How do they capture these images where the ground and background blend together seamlessly. with small lists). This solution may have repeated elements!! @NikitaB it all depends on how good you know LINQ. Returns IEnumerable < Int32 > An IEnumerable<Int32> in C# or IEnumerable (Of Int32) in Visual Basic that contains a range of sequential integral numbers. To get O(k log k) time, you need an array-like structure that supports O(log m) searches and inserts - a balanced binary tree can do this. Use Kyle's approach for an on-line solution. Should X, if theres no evidence for X, be given a non zero probability? However IMHO it is more difficult to read than the foreach loop. My ordersInfo variable has type IEnumerable. I found another simpler solution that doesn't even require the yield ;). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Additional to the valid point from Rick Davin: 1) You can drop the Contains because IndexOf returns -1 if the item is not contained. C# IEnumerable Examples: LINQ, Lists and Arrays - The Developer Blog There is no guarantee that an enumerable always produces the same values each time. How to remove an element from a list by index. Are there good reasons to minimize the number of keywords in a language? Space elevator from Earth to Moon with multiple temporary anchors. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Developers use AI tools, they just dont trust them (Ep. Let's talk about one of my favorite .NET features: IEnumerable. Randomness is about unpredictability and not about shuffling positions in a group. Why does this Curtiss Kittyhawk have a Question Mark in its squadron code? how to give credit for a picture I modified from a scientific article? Should I disclose my academic dishonesty on grad applications? That looks equivalent to me. Find centralized, trusted content and collaborate around the technologies you use most. C# I wouldn't call this LINQ query "simple". Which will actually filter the list based on the criterion given as the predicate, and the list shall get filtered upon the call of the ToList() method, as Where is deferred filtering. How can I do this? The randoms variable is made a HashSet to avoid duplicates being added in the rarest of rarest cases where Random.Next can yield the same value, especially when input list is small. Asking for help, clarification, or responding to other answers. @MartinR Absolutely! How to resolve the ambiguity in the Boy or Girl paradox? In a nutshell, drzaus's simple solution seems to be the best overall, from these three. So if we have a list of 1000 elements, and we want to choose 5 at random, there's no way a standard random number generator will hit all the possibilities. How can we compare expressive power between two Turing-complete languages? It acts upon an IEnumerable sequence. How do they capture these images where the ground and background blend together seamlessly? 1) Is there a better way to return a list of all keys than just doing a foreach on the KeyValuePair List? c# - How to select items from IEnumerable? - Stack Overflow This will only work if OrderBy() only calls the key selector once for each element. start + count -1 is larger than Int32.MaxValue. On average, for K = N/2 (the worst case for Paul's suggested improvement), the (thrashing improved) algorithm appears to take ~0.693*N iterations. It's similar in performance to shuffling the input, but of course allows the sample to be generated without modifying the original data. Having a large list will reduce the odds greatly for duplicates. Well you could definitly use your LINQ. Also noticed that this alters the order of the items being enumerated, which may be acceptable in some situations, but not in others. Exceptions ArgumentOutOfRangeException count is less than 0. The only thing I can thing of is that Random.Next() is pretty slow, and that performance benefits if you generate only one random number for each selected item. Should i refrigerate or freeze unopened canned food items? Do you think IList would be any better? A snippet of the implementation is given below. Given an IEnumerable source and an IEnumerable exceptions, return an IEnumerable result which contains all of source, without exceptions, only omitting exact instances of a value. Let's assume we can combine multiple independent random number generators to create a larger one (. I have an IEnumerable called day. rev2023.7.5.43524. If it is, the next has a 4/39 chance, otherwise it has a 5/39 chance. An IEnumerable in C# or IEnumerable(Of Int32) in Visual Basic that contains a range of sequential integral numbers. Compare to the similar. for (1) you can shuffle a list faster than sorting is, for (2) you will be biasing your distribution by using %, Given the objection you raised about the cycle length of a rng, is there any way we. To learn more, see our tips on writing great answers. This is actually a harder problem than it sounds like, mainly because many mathematically-correct solutions will fail to actually allow you to hit all the possibilities (more on this below). This projection method requires the transform function, selector, to produce one value for each value in the source sequence, source. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. public IEnumerable<UserProfile> GetUsers () { var allDepartments = GetAllDepartments (active: true); // Returns IEnumerable<Department> var allUsers = GetAllUserDepartments (active: true); // Returns IEnumerable<User> var users = allDepartments .Join (allUsers, x => x.Department, y => y.Department, (x, y) => y, StringComparer.OrdinalIgnore. Developers use AI tools, they just dont trust them (Ep. Using VS 2015 and .NET 4.6.1 . In other words, if something is an IEnumerable, you can mostly think of it like an array or a list.You can use a foreach statement to loop through it, you can use LINQ to map or reduce it in a hundred different ways, or you can explicitly cast it to an array with .ToArray() and . It is a lot harder than one would think. The selected answer is great and elegant, but it's not that efficient, given that the time complexity is based on the sample size, not the selection size. asp.net-mvc c#-4.0 ienumerable Share Improve this question Follow Your algorithm and JanDotNet's algorithm will run in \$O(n^2)\$ time. How can I get the data of specific property of the list instead of the objects? Is the difference between additive groups and multiplicative groups just a matter of notation? Therefore as mentioned in the other answer, remember to do a null check before converting it to a List. Given an IEnumerable<T> source and an IEnumerable<T> exceptions, return an IEnumerable<T> result which contains all of source, without exceptions, only omitting exact instances of a value. rev2023.7.5.43524. When an electromagnetic relay is switched on, it shows a dip in the coil current for a millisecond but then increases again. This technique is called selection sampling, a special case of Reservoir Sampling. ToList (); int [] array = result. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Doesn't this pan out to @ersin's rather shorter answer, and won't it fail if you get a repeated random number (Where Ersin's will have a bias towards the first item of a repeated pair). But if the IEnumerable is null, when you try to convert it to a List, you'll get an ArgumentNullException saying Value cannot be null. If you just need to check if there is one or more items in an IEnumerable a more efficient method is to check if there are any. Select is used to transform one object into another or select only specific parts of a given object. If you cast a spell with Still and Silent metamagic, can you do so while wildshaped without natural spell? Connect and share knowledge within a single location that is structured and easy to search. If you are not suppose to add something to the Collection then you should use/return IEnumerable. Do large language models know what they are talking about? Removing from the middle of a list so often will be costly. Where can I find the hit points of armors? Find centralized, trusted content and collaborate around the technologies you use most. : if a value appears twice in source, but once in exceptions, then result will have that value exactly one time. This means that it is perfectly fine to have the following: You can use the extension method AsEnumerable in Assembly System.Core and System.Linq namespace : This will, as said on this MSDN link change the type of the List in compile-time. Any () only check to see there is a value and does not loop through everything. so 't' prefix means temporary? The following code example demonstrates how to use Range to generate a sequence of values. this indeed seems like a bit of a hack.. i tried it and it also didnt compile. Not the answer you're looking for? Using LINQ with large lists (when costly to touch each element) AND if you can live with the possibility of duplicates: For my use i had a list of 100.000 elements, and because of them being pulled from a DB I about halfed (or better) the time compared to a rnd on the whole list. Nice idea, with problems. Comic about an AI that equips its robot soldiers with spears and swords, Convert a 0 V / 3.3 V trigger signal into a 0 V / 5V trigger signal (TTL), Solving implicit function numerically and plotting the solution against a parameter. Enumerable.Count Method (System.Linq) | Microsoft Learn . 4) If K is large compared to N and I invert the sense of the set, then I enumerate all items and test if the index is not in the set. An IEnumerable will have to iterate through every item. I think the order by is O(n log(n)), so I would choose this solution if code simplicity is the main concern (i.e. There is still some thrashing, but much less. Further, if you don't want to modify your initial list, you can write down all your swaps in a temporary list, reverse that list, and apply them again, thus performing the inverse set of swaps and returning you your initial list without changing the O(k) running time. Removing exact instances of elements in one list from another, Why Enumerable.Except() Might Not Work the Way You Might Expect. More info about Internet Explorer and Microsoft Edge, Count(IEnumerable, Func). List implements the IEnumerable interface so it is already an enumerable. index Int32. Comic about an AI that equips its robot soldiers with spears and swords. You may consider using a linked list for an algorithm requiring so many removals. I gather all the indices into a SortedSet, then emit items in sorted index order. From MSDN - IEnumerable.Where. Should i refrigerate or freeze unopened canned food items? You want to use Where which is a deferred filtering. Sorry about that. Draw the initial positions of Mlkky pins in ASCII art, Can the type 3 SS be obtained using the ANOVA function or an adaptation that is readily available in Mathematica. Sounds like the OP is new to LINQ. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. source IEnumerable<TSource> An IEnumerable<T> to return an element from. Since both are generics, you can do like below. How to get value from IEnumerable collection using its Key? The following code example demonstrates how to use Count(IEnumerable) to count the elements in an array. To get values from IEnumerable list individually in c# , vb.net we have different methods Method 1: If you want to get first elements from list we need to write the code like as shown below C# Code var data = dt.AsEnumerable ().Select (row => new { UserId = row ["UserId"].ToString (), UserName = row ["UserName"].ToString (), Name of a movie where a guy is committed to a hospital because he sees patterns in everything and has to make gestures so that the world doesn't end, Defining the second by an alien civilization. Is there a way to sync file naming across environments? Why would the Bank not withdraw all of the money for the check amount I wrote? In python. Connect and share knowledge within a single location that is structured and easy to search. It means that you do not have to convert or cast anything. Think like the SELECT clause of SQL - it changes the output. Safe to drive back home with torn ball joint boot? My solution for the problem of thrashing is this: if K < N/2, do it your way. I need a quick algorithm to select 5 random elements from a generic list. For all the answers below, be aware that you need to have the System.Linq namespace imported. so i want this method to be able to return a List, as well as a Stack, as well as a List etc etc. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic. Developers use AI tools, they just dont trust them (Ep. This appears to be an implementation of the accepted answer. To learn more, see our tips on writing great answers. If you're using Generic version IEnumerable, The conversion is straight forward. Randomly select a specific quantity of indices from an array? // #1: get all keys (remove Distinct () if you don't want it) List<string> allKeys = (from kvp in KV_List select kvp.Key).Distinct ().ToList (); // allKeys = { "qwer", "zxcv", "hjkl" } // #2: get values for a key string key = "qwer"; List<string> values = (from kvp in KV_List where kvp.Key == key select kvp.Value).ToList (); // values = { "asdf. This will give you the benefits also to only enumerate your collection we needed (see MSDN example for this). Hmm. You do if you want the specific methods from the non-generic interface, as some of them are explicitly implemented, or am I'm on the wrong track here? @Fattie This is for cases where shuffling is extremely inefficient (e.g., the list is huge) or you're not permitted to modify the order of the original list. 1) If you need true random values which means there is no restriction on which elements to choose from (ie, once chosen item can be reselected): If you set the exception flag off, then you can choose random items any number of times. If you're using Generic version IEnumerable<T>, The conversion is straight forward. The fact that you replaced good variable names with a bunch of x's, y's and m's does not help either. I implemented it differently though, as I also wanted the result in random order. Do you have any reason not to use new Random() which is based on Environment.TickCount vs. DateTime.Now.Millisecond? Is there a non-combative term for the word "enemy"? What to do to align text with chemfig molecules? The type parameter needs to be specified by the caller somewhere. So for k << n, this can be faster. I was a little surprised no one suggested using Except for this approach as it is more robust(can be applied to string and int). Difference between machine language and machine code, maybe in the C64 community? Arent all stack variables temporary? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Learn more about Stack Overflow the company, and our products. The best answers are voted up and rise to the top, Not the answer you're looking for? And TakeWhile, a more complex form of Take, accepts the first elements while a predicate method returns true. What are the advantages and disadvantages of making types as a first class value? You can see here that I have not reordered anything at all when count becomes equal to source.Count. You should use the LongCount method when you expect and want to allow the result to be greater than MaxValue. Get up to $15 back via rebate. The immediate return value is an object that stores all the information that is required to perform the action. Order is a custom object. JVM bytecode instruction struct with serializer & parser. You need to add a generic type parameter to your method: public IEnumerable<T> ReturnSomething<T> () { Stack<T> stackOfT = new Stack<T> (); return stackOfT; } The type parameter appears after the method name, but before the parameters. When an electromagnetic relay is switched on, it shows a dip in the coil current for a millisecond but then increases again. Parameters. 3) If you need truly distinct random values from your group by taking into account the duplicates in the original group, then you may use the same approach as above, but a HashSet will be lighter than a dictionary. Thus I compose a list of the indices to NOT keep. Convert from List into IEnumerable format Ask Question Asked 12 years, 5 months ago Modified 4 years, 6 months ago Viewed 351k times 128 IEnumerable<Book> _Book_IE List<Book> _Book_List How shall I do in order to convert _Book_List into IEnumerable format? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. How shall I do in order to convert _Book_List into IEnumerable format? Filters a sequence of values based on a predicate. You need to add a generic type parameter to your method: The type parameter appears after the method name, but before the parameters. Are MSO formulae expressible as existential SO formulae over arbitrary structures? choices of k element subset out of n elements [this is an approximation of (n choose k)]. It is like a dictionary but you can get the values as IEnumerable with the same key. I used the AsEnumerable extension method to come around this. It sounds like you want the Where statement, not the Select statement. How do laws against computer intrusion handle the modern situation of devices routinely being under the de facto control of non-owners? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Why a kite flying at 1000 feet in "figure-of-eight loops" serves to "multiply the pulling effect of the airflow" on the ship to which it is attached? msdn.microsoft.com/en-us/library/vstudio/, http://en.wikipedia.org/wiki/Fisher-Yates_shuffle, Guids are guaranteed to be unique, not random, Return random subset of N elements of a given array, http://krkadev.blogspot.com/2010/08/random-numbers-without-repetition.html. It is also possible to have a method with more than one type parameter.