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58
votes
26answers
9k views
21
votes
5answers
9k views

What's the use of .Any() in a C# List<>?

I've been discussing this with colleagues, and we couldn't figure out what the use is of .Any for any given List<>, in C#. You can check the validity of an element in the array like the ...
14
votes
2answers
37k views

Should I use a list or an array?

I'm working on a windows form to calculate UPC for item numbers. I successfully create one that will handle one item number/UPC at a time, now I want to expand and do it for multiple item numbers/...
13
votes
4answers
1k views

Why are cons lists associated with functional programming?

I have noticed that most functional languages employ a singly-linked list (a "cons" list) as their most fundamental list types. Examples include CLisp, Haskell and F#. This is different to mainstream ...
12
votes
8answers
4k views

Find a “hole” in a list of numbers

What is the fastest way to find the first (smallest) integer that doesn't exist in a given list of unsorted integers (and that is greater than the list's smallest value)? My primitive approach is ...
10
votes
1answer
5k views

C++11 support for higher-order list functions

Most functional programming languages (e.g. Common Lisp, Scheme / Racket, Clojure, Haskell, Scala, Ocaml, SML) support some common higher-order functions on lists, such as map, filter, takeWhile, ...
9
votes
1answer
592 views

Origin of common list-processing function names

Some higher-order functions for operating on lists or arrays have been repeatedly adopted or reinvented. The functions map, fold[l|r], and filter are found together in several programming ...
7
votes
3answers
444 views

Is there a language where collections can be used as objects without altering the behavior?

Is there a language where collections can be used as objects without altering the behavior? As an example, first, imagine those functions work: function capitalize(str) //suppose this *modifies*...
7
votes
6answers
12k views

How do I figure out the minimum number of swaps to sort a list in-place?

In-place sorting is essentially swapping elements without using extra storage, correct? How can I find the minimum number of swaps required for a list? A C D Q R Z E // input | | | > > >...
6
votes
1answer
1k views

Why appending to a list in Scala should have O(n) time complexity?

I am learning Scala at the moment and I just read that the execution time of the append operation for a list (:+) grows linearly with the size of the list. Appending to a list seems like a pretty ...
5
votes
2answers
3k views

Why does java collections not supply a function for the index of max value?

I have been using Collections.max(list) for many projects, but I occasionally want to find the index of that maximum element. I feel silly writing a function to do this for myself in every program I ...
5
votes
3answers
2k views

Use Queue<T> or stick to native f# lists

I need something that represents a queue in F#. The queue will be filled with items once, and (as the application progresses) items will be taken from this queue and moved to other lists. Should I ...
5
votes
7answers
537 views

Test driven development when implementing a flexible length list

According to the commonly used TDD strategy, to implement something, you write a test that fail the code first, write the simplest code, refactor, and then repeat. I am trying to imagine this scenario ...
4
votes
3answers
1k views

Lisp: Benefits of lists as code over arrays as code?

Question for lisp programmers: Lisp code is lisp data, usually lists. Is there an advantage to code being lists over code being arrays? Would macros be easier to write/faster to run? You can ...
4
votes
2answers
339 views

Is this data model a list or tree?

Using python syntax with below environment diagram, teacher taught us that there are 11 trees(orange boundary) in this diagram, including leaf. It has been taught here, lists are represented as a ...
4
votes
3answers
145 views

Is storing data directly in a list node better than storing a pointer to data?

Suppose we have two different doubly-linked list structures: One has content of the node embedded directly in the node: struct Content { // some stuff }; struct Node { struct Node *next; ...
4
votes
1answer
74 views

Performance of list concatenation followed by scanning

Consider the following code snippet: -- list_1 = [1, 2, 3] -- list_2 = [4, 5, 6] final_list = list_1 ++ list_2 result = map (+1) final_list Is the time spent by it proportional just to the length ...
4
votes
1answer
190 views

JavaScript functional conversion from flat list to tree

I've been going through the RxJS tutorials http://reactivex.io/learnrx/. Almost all of the exercises involve moving from a hierarchical structure to a flat structure so I thought I'd try to do the ...
4
votes
1answer
185 views

Tail-recursive implementation of take-while

I am trying to write a tail-recursive implementation of the function take-while in Scheme (but this exercise can be done in another language as well). My first attempt was (define (take-while p xs) ...
4
votes
2answers
420 views

Is this the right strategy to convert an in-level order binary tree to a doubly linked list?

So I recently came across this question - Make a function that converts a in-level-order binary tree into a doubly linked list. Apparently, it's a common interview question. This is the strategy I ...
3
votes
3answers
2k views

Best way to choose random element from weighted list

I want to create a simple game. Every so often, a power up should appear. Right now the different kinds of power ups are stored in an array. However, not every power up should appear equally often: ...
3
votes
3answers
92 views

Is it odd if Nodes in a LinkedList held references to the List object?

Its like, I want to call .moveToBefore(Node) on a Node object and have the node relocate to before the node passed in. The problem arises if the node passed in is the head node. The List object will ...
3
votes
1answer
169 views

What data type is this?

I have a list of items I am adding to, however this special list will delete anything past a given capacity. Note the order is maintained. For the life of me, I can't think of the name of such a ...
3
votes
1answer
442 views

Why is iterating through List<T> more expensive than iterating through Array in .NET?

According to the answers in this post, List<T> is backed by an Array. According to this article, list iteration is considerably slower than array iteration. If Lists are arrays 'under the hood',...
3
votes
5answers
136 views

Conditionally initializing a string list

I am writing a program that needs to be able to process data from a number of different sources. The sources output data in a variety of formats. So, depending on which source is being used, I need to ...
3
votes
1answer
107 views

Why use atomic vectors or matrices in R at all?

In reading Hadley Wickham's Advanced R I learned about the difference between atomic vectors and lists; and matrices/arrays and dataframes. This is something I hadn't really appreciated before, and ...
3
votes
2answers
49 views

Implementing a key-sensitive monad bind for key-value Map

Based on the List monad I set out to define Monad instances for the Map type from Data.Map, to perform chained unions and folds on Maps like lists, but with the efficient sorting and merging of Maps: ...
2
votes
3answers
345 views

Why it is `(cons 1 (cons 2 (cons 3 nil)))` and not `(cons 3 (cons 2 (cons 1 nil)))` for [1,2,3]?

Is there any special reason that to construct list in Scheme you use (cons 1 (cons 2 (cons 3 nil))) instead of (cons 3 (cons 2 (cons 1 nil))) ? While the first seems more obvious because it ...
2
votes
3answers
208 views

Functional programming: Compare all items in an array

In functional programming, how do I do an equality comparison of all items in an array? I have an array of items that I want to compare, for example for equality. Is it possible to use a fold (also ...
2
votes
2answers
680 views

Mapping a list of optional values to an optional list of values

I have encountered the following pattern while programming in Haskell (but the pattern could occur in any language supporting lists, option types, and mapping of a function over a list). I have types ...
2
votes
3answers
290 views

What language has integrated “list insertion” as part of code *syntax*?

Many programming languages permit natural manipulation of strings, and some languages permit the manipulations of lists too. More often then not (always?), these operations are done as procedure ...
2
votes
2answers
119 views

Designing a user-defined list to be stored in a relational database - Should I include user index?

By index, I mean, as the user creates the list, each item receives an integer index for its place in that particular list. Since there will be a table of ListItems, I'd prefer to avoid using the name ...
2
votes
1answer
142 views

When should I use a generator and when a list in Python? [duplicate]

I often find it cleaner to write a generator than to return a list. For example, I prefer def my_func_gen(foo): for i in foo: # Do some stuff that's too complicated for a list or ...
2
votes
1answer
682 views

Maintain ordered collection by updating as few `order` fields as possible

I'm working on integrating a reorderable lists UI widget with a Meteor.js (MongoDB, in effect) collection: { order: ???, // what type to use here? property1: ..., ... propertyN: ... } Each ...
2
votes
2answers
571 views

Designing a list class with filtering and sorting

The app I'm developing needs to display lists of items. Simple enough, but there are a number of things which can change based on user input: Items can be added to/removed from the list. The items ...
1
vote
3answers
449 views

What can Go chan do that a list cannot?

I want to know in which situation Go chan makes code much simpler than using list or queue or array that is usually available in all languages. As it was stated by Rob Pike in one of his speeches ...
1
vote
2answers
98 views

Load to list in one loop and then process list in another or do it all at once

I have a dataset full of rows that I must initialize into myclass and then process. I am currently looping through each row in the dataset, initializing a new instance of myclass, then adding that ...
1
vote
2answers
1k views

Why a hashtable? Why not just a non-hashed associative array?

I've been learning about using a hashtable to efficiently check for items in a list without looping through the whole thing, but there's one thing that I don't get: Why hashed keys? It seems like: ...
1
vote
3answers
125 views

Logic Programming(Unification) vs List Comprehensions (in Functional Programming)

I found this answer on StackOverflow very clear to explain the difference beween the Logic Programming paradigm and the Functional Programming paradigm: The thing that makes logical append ...
1
vote
2answers
169 views

Building a sequential list in languages with cons/linked lists

In languages where cons lists are a major datatype, it is very easy to create a list from last to first by prepending items. When doing processing from some input file, however, one is most likely to ...
1
vote
2answers
576 views

Multiple orders in a single list

I have a problem with a ranking system I am using. Scenario: An online game with around 10k players calculates a real time ranking of points when a certain event occurs. Events don't occur that ...
1
vote
4answers
76 views

Obtaining lists from an array

Let's say my array contains integers. I'd like to create lists, so that every list contains indexes where a particular value occured in the array. For instance, if the array was 5,0,3,5,2,5,3, we ...
1
vote
2answers
99 views

Is python list comprehension using multi-threading or parallelized in any way by default?

When I write... l2 = [my_computation(x) for x in l] ..., I wonder if python is applying my_computation to every x using all cores of my CPU. If not, why ? Is there a simple way to make python ...
1
vote
1answer
94 views

Using a list of tuples vs a list of custom objects

I have a situation where I have several text documents and I want to create a list that contains the words in those documents. But I also need to record several properties of each word. These ...
1
vote
1answer
584 views

Custom Alphabetic Sorting of Array in Java

I have a requirement to read a text file with lines in tag=value format and then output the file with specific tags listed first and the rest sorted alphabetically. The incoming file is randomly ...
1
vote
3answers
486 views

Random List of numbers in C

I have just started a C programming course and so far have only done the basics like printf, read a little on variables etc on the course book. The teacher has tasked us with writing a program that ...
1
vote
2answers
439 views

What does using (vec col) or (vector arg1 & args) cost?

I am working through some Lisp exercises using Clojure. If I were to convert Lisp lists to Clojure vectors, solving some of the problems would be simpler, so here is my question: Does using vec or ...
1
vote
0answers
241 views

Performance of a Skip-List algorithm

Here is a simple code for a randomized skip-list: Coin_Side flip() { if ( random() % 2 == 0 ) return HEADS; else return TAILS; } Note: random() returns an integer that uses ...
1
vote
0answers
315 views

What is the rule on passing around collections? List vs. Ienumerable vs. IQueryable

I do Entity Framework stuff using repository patterns that are passed to the controller to than be called by the client using jquery AJAX.. Is there any basic rules on in what format I should be ...
0
votes
3answers
146 views

Why don't empty iterables in python raise Exceptions when you try to iterate over them [duplicate]

I find this behaviour in Python quite peculiar and I believe it can lead to many bugs especially if you have a function/method that takes in a list and returns another list after carrying out some ...