All Questions
8,242
questions
2122
votes
26
answers
1.3m
views
How do I check if a variable is an array in JavaScript?
How do I check if a variable is an array in JavaScript?
if (variable.constructor == Array)
- 38.1k
1297
votes
25
answers
2.0m
views
Converting array to list in Java
How do I convert an array to a list in Java?
I used the Arrays.asList() but the behavior (and signature) somehow changed from Java SE 1.4.2 (docs now in archive) to 8 and most snippets I found on the ...
- 25.5k
756
votes
11
answers
1.4m
views
Convert list to array in Java [duplicate]
How can I convert a List to an Array in Java?
Check the code below:
ArrayList<Tienda> tiendas;
List<Tienda> tiendasList;
tiendas = new ArrayList<Tienda>();
Resources res = this....
- 12.1k
755
votes
16
answers
418k
views
Array versus List<T>: When to use which?
MyClass[] array;
List<MyClass> list;
What are the scenarios when one is preferable over the other? And why?
- 36.1k
618
votes
17
answers
2.4m
views
568
votes
7
answers
249k
views
What are the advantages of NumPy over regular Python lists?
What are the advantages of NumPy over regular Python lists?
I have approximately 100 financial markets series, and I am going to create a cube array of 100x100x100 = 1 million cells. I will be ...
- 24.4k
482
votes
9
answers
1.3m
views
How to declare and add items to an array in Python
I'm trying to add items to an array in Python.
I run
array = {}
Then, I try to add something to this array by doing:
array.append(valueToBeInserted)
There doesn't seem to be an .append method for ...
- 5,809
452
votes
11
answers
376k
views
Python list vs. array – when to use?
If you are creating a 1d array, you can implement it as a list, or else use the 'array' module in the standard library. I have always used lists for 1d arrays.
What is the reason or circumstance ...
- 59.7k
403
votes
32
answers
347k
views
Array or List in Java. Which is faster?
I have to keep thousands of strings in memory to be accessed serially in Java. Should I store them in an array or should I use some kind of List ?
Since arrays keep all the data in a contiguous chunk ...
- 15k
352
votes
4
answers
151k
views
Difference between List and Array types in Kotlin
What is the difference between List and Array types?
It seems can make same operations with them (loops, filter expression, etc..), is there any difference in behavior or usage?
val names1 = listOf("...
- 7,464
340
votes
11
answers
668k
views
Conversion of System.Array to List
Last night I had dream that the following was impossible. But in the same dream, someone from SO told me otherwise. Hence I would like to know if it it possible to convert System.Array to List
Array ...
- 3,971
337
votes
5
answers
247k
views
Is the order of elements in a JSON list preserved?
I've noticed the order of elements in a JSON object not being the original order.
What about the elements of JSON lists? Is their order maintained?
- 9,029
306
votes
9
answers
162k
views
How is Python's List Implemented?
Is it a linked list, an array? I searched around and only found people guessing. My C knowledge isn't good enough to look at the source code.
- 46.1k
298
votes
11
answers
1.0m
views
Initialising an array of fixed size in Python [duplicate]
I would like to know how i can initialize an array(or list), yet to be populated with values, to have a defined size.
For example in C:
int x[5]; /* declared without adding elements*/
How do I do ...
- 3,273
285
votes
9
answers
690k
views
Initializing a list to a known number of elements in Python [duplicate]
Right now I am using a list, and was expecting something like:
verts = list (1000)
Should I use array instead?
- 323k
260
votes
16
answers
268k
views
When to use a linked list over an array/array list?
I use a lot of lists and arrays but I have yet to come across a scenario in which the array list couldn't be used just as easily as, if not easier than, the linked list. I was hoping someone could ...
- 7,522
256
votes
15
answers
257k
views
Performance of Arrays vs. Lists
Say you need to have a list/array of integers which you need iterate frequently, and I mean extremely often. The reasons may vary, but say it's in the heart of the inner most loop of a high volume ...
- 25.7k
225
votes
34
answers
280k
views
Build tree array from flat array in javascript
I have a complex json file that I have to handle with javascript to make it hierarchical, in order to later build a tree.
Every entry of the json has :
id : a unique id,
parentId : the id of the ...
- 2,489
223
votes
7
answers
1.2m
views
How to read a text file into a list or an array with Python [duplicate]
I am trying to read the lines of a text file into a list or array in python. I just need to be able to individually access any item in the list or array after it is created.
The text file is ...
- 2,255
218
votes
6
answers
323k
views
How do you concatenate Lists in C#?
If I have:
List<string> myList1;
List<string> myList2;
myList1 = getMeAList();
// Checked myList1, it contains 4 strings
myList2 = getMeAnotherList();
// Checked myList2, it contains 6 ...
- 5,339
181
votes
10
answers
81k
views
Is there a performance impact when calling ToList()?
When using ToList(), is there a performance impact that needs to be considered?
I was writing a query to retrieve files from a directory, which is the query:
string[] imageArray = Directory.GetFiles(...
- 8,816
171
votes
10
answers
10k
views
Is there a way to measure how sorted a list is?
Is there is a way to measure how sorted a list is?
I mean, it's not about knowing if a list is sorted or not (boolean), but something like a ratio of "sortness", something like the coefficient of ...
- 1,934
163
votes
8
answers
34k
views
Why array implements IList?
See the definition of System.Array class
public abstract class Array : IList, ...
Theoretically, I should be able to write this bit and be happy
int[] list = new int[] {};
IList iList = (IList)list;...
- 35.7k
162
votes
3
answers
85k
views
Difference between Array and List in scala
In what cases I should use Array(Buffer) and List(Buffer). Only one difference that I know is that arrays are nonvariant and lists are covariant. But what about performance and some other ...
- 7,179
161
votes
6
answers
202k
views
How to return a part of an array in Ruby?
With a list in Python I can return a part of it using the following code:
foo = [1,2,3,4,5,6]
bar = [10,20,30,40,50,60]
half = len(foo) / 2
foobar = foo[:half] + bar[half:]
Since Ruby does ...
- 4,741
158
votes
8
answers
310k
views
How to check if element in groovy array/hash/collection/list?
How do I figure out if an array contains an element?
I thought there might be something like [1, 2, 3].includes(1) which would evaluate as true.
- 2,748
141
votes
4
answers
358k
views
Flatten list of lists [duplicate]
I'm having a problem with square brackets in Python. I wrote a code that produces the following output:
[[180.0], [173.8], [164.2], [156.5], [147.2], [138.2]]
But I would like to perform some ...
- 1,695
130
votes
5
answers
124k
views
Create mutable List from array?
I have an array I'd like to turn into a List, in order to modify the contents of the array.
Stack Overflow has plenty of questions/answers that address Arrays.asList() and how it only provides a List ...
- 25.6k
124
votes
7
answers
122k
views
Why are lists used infrequently in Go?
Is there a way to create an array/slice in Go without a hard-coded array size? Why is List ignored?
In all the languages I've worked with extensively: Delphi, C#, C++, Python - Lists are very ...
- 11.2k
120
votes
1
answer
133k
views
Convert 2d numpy array into list of lists [duplicate]
I use an external module (libsvm), which does not support numpy arrays, only tuples, lists and dicts. But my data is in a 2d numpy array. How can I convert it the pythonic way, aka without loops.
&...
- 34.3k
109
votes
6
answers
644k
views
List to array conversion to use ravel() function
I have a list in python and I want to convert it to an array to be able to use ravel() function.
- 1,559
107
votes
6
answers
13k
views
How do arrays in C# partially implement IList<T>?
So as you may know, arrays in C# implement IList<T>, among other interfaces. Somehow though, they do this without publicly implementing the Count property of IList<T>! Arrays have only a ...
- 12.5k
102
votes
8
answers
63k
views
List<T>.Contains() is very slow?
Could anyone explain me why the generics List.Contains() function is so slow?
I have a List<long> with about a million numbers, and the code that is constantly checking if there's a specific ...
- 1,031
102
votes
4
answers
127k
views
Convert an array into an ArrayList [duplicate]
I'm having a lot of trouble turning an array into an ArrayList in Java. This is my array right now:
Card[] hand = new Card[2];
"hand" holds an array of "Cards". How this would look like as an ...
- 1,177
92
votes
8
answers
175k
views
Conversion from List<T> to array T[]
Is there a short way of converting a strongly typed List<T> to an Array of the same type, e.g.: List<MyClass> to MyClass[]?
By short i mean one method call, or at least shorter than:
...
- 10.3k
86
votes
3
answers
225k
views
Python Array with String Indices
Is it possible to use strings as indices in an array in python?
For example:
myArray = []
myArray["john"] = "johns value"
myArray["jeff"] = "jeffs value"
print myArray["john"]
- 11.5k
77
votes
11
answers
47k
views
Arrays.asList() not working as it should?
I have a float[] and i would like to get a list with the same elements. I could do the ugly thing of adding them one by one but i wanted to use the Arrays.asList method. There is a problem though. ...
- 11.6k
77
votes
10
answers
112k
views
find out the elements of an arraylist which is not present in another arraylist
I have to find a best way to find out that elements which is not presented in the second arraylist.
suppose
Arraylist a,b,
Arraylist a={1,2,3,4,5};
Arraylist b={2,3,4};
So basically what I want ...
- 2,350
77
votes
17
answers
31k
views
Easiest way to Rotate a List in c#
Lists say I have a list List<int> {1,2,3,4,5}
Rotate means:
=> {2,3,4,5,1} => {3,4,5,1,2} => {4,5,1,2,3}
Maybe rotate is not the best word for this, but hope you understand what I ...
- 8,853
76
votes
8
answers
240k
views
How can I create an array/list of dictionaries in python?
I have a dictionary as follows:
{'A':0,'C':0,'G':0,'T':0}
I want to create an array with many dictionaries in it, as follows:
[{'A':0,'C':0,'G':0,'T':0},{'A':0,'C':0,'G':0,'T':0},{'A':0,'C':0,'G':0,...
- 761
74
votes
3
answers
153k
views
how to flatten a 2D list to 1D without using numpy? [duplicate]
I have a list looks like this:
[[1,2,3],[1,2],[1,4,5,6,7]]
and I want to flatten it into [1,2,3,1,2,1,4,5,6,7]
is there a light weight function to do this without using numpy?
- 1,001
71
votes
3
answers
54k
views
JavaScript filter that stops at the first result
Is there a mechanism in JavaScript (without having to write my own) similar to filter. Instead of returning all the filtered elements of a collection though, it only returns the first one. Of course I ...
- 51.8k
71
votes
10
answers
136k
views
How to create a numpy array of lists?
I want to create a numpy array in which each element must be a list, so later I can append new elements to each.
I have looked on google and here on stack overflow already, yet it seems nowhere to be ...
- 1,203
70
votes
7
answers
98k
views
Assign value to an individual cell in a two dimensional python array [duplicate]
Let's say I have the following empty two dimensional array in Python:
q = [[None]*5]*4
I want to assign a value of 5 to the first row in the first column of q. Instinctively, I do the following:
q[...
- 32.5k
70
votes
5
answers
15k
views
How to compare equality of lists of arrays with modern Java?
I have two lists of arrays.
How do I easily compare equality of these with Java 8 and its features, without using external libraries? I am looking for a "better" (higher-level, shorter, more ...
- 61.8k
69
votes
8
answers
430k
views
Working with a List of Lists in Java
I'm trying to read a CSV file into a list of lists (of strings), pass it around for getting some data from a database, build a new list of lists of new data, then pass that list of lists so it can be ...
Rob-0
69
votes
7
answers
98k
views
What is the shortest way to initialize List of strings in java?
I am searching for the shortest way (in code) to initialize list of strings and array of strings, i.e. list/array containing
"s1", "s2", "s3" string elements.
- 12.9k
67
votes
7
answers
54k
views
Reserve memory for list in Python?
When programming in Python, is it possible to reserve memory for a list that will be populated with a known number of items, so that the list will not be reallocated several times while building it? ...
- 68k
65
votes
7
answers
185k
views
An array of List in c#
I want to have an array of Lists.
In c++ I do like:
List<int> a[100];
which is an array of 100 Lists. each list can contain many elements.
I don't know how to do this in c#. Can anyone help me?...
- 3,635
65
votes
11
answers
20k
views
Can I create a "view" on a Python list?
I have a large list l. I want to create a view from element 4 to 6. I can do it with sequence slice.
>>> l = range(10)
>>> lv = l[3:6]
>>> lv
[3, 4, 5]
However lv is a copy ...
- 18.4k