All Questions
4,391
questions
5432
votes
28
answers
4.4m
views
How to access the index value in a 'for' loop?
How do I access the index while iterating over a sequence with a for loop?
xs = [8, 23, 45]
for x in xs:
print("item #{} = {}".format(index, x))
Desired output:
item #1 = 8
item #2 = ...
- 323k
698
votes
40
answers
258k
views
How to iterate over a list in chunks
I have a Python script which takes as input a list of integers, which I need to work with four integers at a time. Unfortunately, I don't have control of the input, or I'd have it passed in as a list ...
- 55.7k
610
votes
28
answers
562k
views
How to remove elements from a generic list while iterating over it?
I am looking for a better pattern for working with a list of elements which each need processed and then depending on the outcome are removed from the list.
You can't use .Remove(element) inside a ...
- 10.8k
511
votes
15
answers
555k
views
How can I avoid "RuntimeError: dictionary changed size during iteration" error?
Suppose I have a dictionary of lists:
d = {'a': [1], 'b': [1, 2], 'c': [], 'd':[]}
Now I want to remove key-value pairs where the values are empty lists. I tried this code:
for i in d:
if not d[i]...
- 26.4k
309
votes
7
answers
659k
views
How do I loop through a list by twos? [duplicate]
I want to loop through a Python list and process 2 list items at a time. Something like this in another language:
for(int i = 0; i < list.length(); i+=2)
{
// do something with list[i] and list[...
- 81.4k
160
votes
9
answers
285k
views
How to for_each through a list(objects) in Terraform 0.12
I need to deploy a list of GCP compute instances. How do I loop for_each through the "vms" in a list of objects like this:
"gcp_zone": "us-central1-a",
"...
- 2,671
156
votes
4
answers
238k
views
Check if list<t> contains any of another list
I have a list of parameters like this:
public class parameter
{
public string name {get; set;}
public string paramtype {get; set;}
public string source {get; set;}
}
IEnumerable<...
- 8,122
148
votes
6
answers
174k
views
Iterate through adjacent pairs of items in a Python list [duplicate]
Is it possible to iterate a list in the following way in Python (treat this code as pseudocode)?
a = [5, 7, 11, 4, 5]
for v, w in a:
print [v, w]
And it should produce
[5, 7]
[7, 11]
[11, 4]
[4, ...
- 3,509
145
votes
7
answers
210k
views
Python : List of dict, if exists increment a dict value, if not append a new dict
I would like do something like that.
list_of_urls = ['http://www.google.fr/', 'http://www.google.fr/',
'http://www.google.cn/', 'http://www.google.com/',
'http://www....
- 17.7k
142
votes
5
answers
263k
views
Iterating Over Dictionary Key Values Corresponding to List in Python
Working in Python 2.7. I have a dictionary with team names as the keys and the amount of runs scored and allowed for each team as the value list:
NL_East = {'Phillies': [645, 469], 'Braves': [599, ...
- 2,223
118
votes
6
answers
165k
views
Loop through list with both content and index [duplicate]
It is very common for me to loop through a python list to get both the contents and their indexes. What I usually do is the following:
S = [1,30,20,30,2] # My list
for s, i in zip(S, range(len(S))):
...
- 5,449
118
votes
3
answers
140k
views
Extract list of attributes from list of objects in python
I have an uniform list of objects in python:
class myClass(object):
def __init__(self, attr):
self.attr = attr
self.other = None
objs = [myClass (i) for i in range(10)]
Now I ...
- 1,407
101
votes
12
answers
24k
views
Strange result when removing item from a list while iterating over it in Python
I've got this piece of code:
numbers = list(range(1, 50))
for i in numbers:
if i < 20:
numbers.remove(i)
print(numbers)
But, the result I'm getting is:
[2, 4, 6, 8, 10, 12, 14, 16, ...
- 3,676
85
votes
6
answers
429k
views
Creating a list of objects in Python
I'm trying to create a Python script that opens several databases and compares their contents. In the process of creating that script, I've run into a problem in creating a list whose contents are ...
77
votes
7
answers
157k
views
Modifying list while iterating [duplicate]
l = range(100)
for i in l:
print i,
print l.pop(0),
print l.pop(0)
The above python code ...
- 22.7k
61
votes
3
answers
60k
views
LINQ: How to skip one then take the rest of a sequence
i would like to iterate over the items of a List<T>, except the first, preserving the order. Is there an elegant way to do it with LINQ using a statement like:
foreach (var item in list.Skip(...
- 15.4k
60
votes
2
answers
128k
views
Groovy, how to iterate a list with an index
With all the shorthand ways of doing things in Groovy, there's got to be an easier way to iterate a list while having access to an iteration index.
for(i in 0 .. list.size()-1) {
println list.get(...
- 31.7k
59
votes
6
answers
109k
views
Change a value in mutable list in Kotlin
I got this mutablelist:
[Videos(id=4, yt_id=yRPUkDjwr1A, title=test4, likes=0, kat=pranks, ilike=false), Videos(id=3, yt_id=WkyUU9ZDUto, title=test3, likes=0, kat=pranks, ilike=false), Videos(id=2, ...
- 1,178
57
votes
8
answers
74k
views
Process a list with a loop, taking 100 elements each time and automatically less than 100 at the end of the list
Is there a way to use a loop that takes the first 100 items in a big list, does something with them, then the next 100 etc but when it is nearing the end it automatically shortens the "100" step to ...
- 983
40
votes
5
answers
46k
views
Can't modify list elements in a loop [duplicate]
While looping over a list in Python, I was unable to modify the elements without a list comprehension.
For reference:
li = ["spam", "eggs"]
for i in li:
i = "foo"
li
...
- 681
40
votes
6
answers
105k
views
Better/Faster to Loop through set or list?
If I have a python list that is has many duplicates, and I want to iterate through each item, but not through the duplicates, is it best to use a set (as in set(mylist), or find another way to create ...
- 45.8k
35
votes
4
answers
13k
views
Loop over 2 lists, repeating the shortest until end of longest [duplicate]
I am sure there is an easy and obvious way to do this, but I have been googling and reading the docs and I just cannot find anything.
This is what I want to achieve:
la = ['a1', 'a2', 'a3', 'a4']
lb ...
- 1,600
34
votes
3
answers
4k
views
Modify list and dictionary during iteration, why does it fail on dict?
Let's consider this code which iterates over a list while removing an item each iteration:
x = list(range(5))
for i in x:
print(i)
x.pop()
It will print 0, 1, 2. Only the first three ...
- 1,332
32
votes
4
answers
25k
views
Iterating over two lists one after another
I have two lists list1 and list2 of numbers, and I want to iterate over them with the same instructions. Like this:
for item in list1:
print(item.amount)
print(item.total_amount)
for item in ...
- 1,180
30
votes
9
answers
24k
views
Removing Item From List - during iteration - what's wrong with this idiom? [duplicate]
As an experiment, I did this:
letters=['a','b','c','d','e','f','g','h','i','j','k','l']
for i in letters:
letters.remove(i)
print letters
The last print shows that not all items were removed ? (...
- 6,055
29
votes
4
answers
49k
views
How can you split a list every x elements and add those x amount of elements to an new list?
I have a list of multiple integers and strings
['-200', ' 0', ' 200', ' 400', ' green', '0', '0', '200', '400', ' yellow', '200', '0', '200', '400', ' red']
I'm having difficulty separating the ...
- 1,993
24
votes
1
answer
34k
views
lapply function /loops on list of lists R
I know this topic appeared on SO a few times, but the examples were often more complicated and I would like to have an answer (or set of possible solutions) to this simple situation. I am still ...
- 1,083
23
votes
3
answers
111k
views
Building a list in a loop in R - getting item names correct
I have a function which contains a loop over two lists and builds up some calculated data. I would like to return these data as a lists of lists, indexed by some value, but I'm getting the assignment ...
- 563
22
votes
3
answers
32k
views
Put multiple data frames into list (smart way) [duplicate]
Is it possible to put a lot of data frames into a list in some easy way?
Meaning instead of having to write each name manually like the following way:
list_of_df <- list(data_frame1,data_frame2,...
- 2,257
21
votes
7
answers
46k
views
Removing Items in a List While Iterating Through It with For Each Loop
I have a list named NeededList I need to check each item in this list to see if it exists in my database. If it does exist in the database I need to remove it from the list. But I can't change the ...
- 587
20
votes
2
answers
71k
views
Create array of json objects using for loops
I'm attempting to extract values from an html and then convert them into a json array, and so far I have been able to get what I want, but only as separate strings:
I did two for loops:
for line in ...
- 203
19
votes
6
answers
9k
views
Python strange behavior with enumerate
I know I'm not supposed to modify the list inside a loop, but just out of curiosity, I would like to know why the number of iterations is different between the following two examples.
Example 1:
x = ...
- 355
17
votes
9
answers
39k
views
How to loop through the alphabet via underscoreJS
I'm using Underscore's template() method in BackboneJS views. I'd like to show a list of alphabet letters in my view in order to sort a collection by letter.
As a result, I have a list of 26 links (...
- 713
17
votes
5
answers
99k
views
Assigning values to variables in a list using a loop
var_list = [one, two, three]
num = 1
for var in var_list:
var = num
num += 1
The above gives me an error that 'one' doesn't exist. Can you not assign in this way? I want to assign an ...
- 18k
16
votes
6
answers
16k
views
How to flatten all items from a nested Java Collection into a single List?
Given a complex nested collection of objects such as:
Set<List<Map<String, List<Object>>>> complexNestedCollection;
Does a generic method exist to flatten this out and get a ...
- 38.2k
16
votes
4
answers
52k
views
How to use tqdm to iterate over a list
I would like to know how long it takes to process a certain list.
for a in tqdm(list1):
if a in list2:
#do something
but this doesnt work. If I use for a in tqdm(range(list1)) i wont be ...
- 1,353
16
votes
5
answers
49k
views
Java iterate over ArrayList with HashMap in it
I have a Hashmap with four answers. And I have for ex 2 questions. This is how i do it
// Awnsers question 1
antwoorden1.put("Hypertext Preprocessor", true);
antwoorden1.put("Hypertext ...
- 245
16
votes
3
answers
25k
views
replace index values in pandas dataframe with values from list
I have a dataframe and 2 lists.
the 1st list gives a set of index values from the dataframe I want to replace
the 2nd list gives the values I want to use
I don't want to touch any of the other ...
- 1,117
16
votes
4
answers
24k
views
Access list element using get()
I'm trying to use get() to access a list element in R, but am getting an error.
example.list <- list()
example.list$attribute <- c("test")
get("example.list") # Works just ...
- 23.3k
16
votes
6
answers
18k
views
Iterate over a dict or list in Python
Just wrote some nasty code that iterates over a dict or a list in Python. I have a feeling this was not the best way to go about it.
The problem is that in order to iterate over a dict, this is the ...
- 49.6k
16
votes
6
answers
509
views
Traversing a list of lists by index within a loop, to reformat strings
I have a list of lists that looks like this, that was pulled in from a poorly formatted csv file:
DF = [['Customer Number: 001 '],
['Notes: Bought a ton of stuff and was easy to deal with'],
['...
- 12.3k
15
votes
4
answers
15k
views
Remove elements as you traverse a list in Python [duplicate]
In Java I can do by using an Iterator and then using the .remove() method of the iterator to remove the last element returned by the iterator, like this:
import java.util.*;
public class ...
- 31k
15
votes
4
answers
198k
views
Why do I get "List index out of range" when trying to add consecutive numbers in a list using "for i in list"? [duplicate]
Given the following list
a = [0, 1, 2, 3]
I'd like to create a new list b, which consists of elements for which the current and next value of a are summed. It will contain 1 less element than a.
Like ...
- 7,334
15
votes
3
answers
15k
views
How to iterate in a cartesian product of lists
I would like to iterate in a for loop using 3 (or any number of) lists with any number of elements, for example:
from itertools import izip
for x in izip(["AAA", "BBB", "CCC"], ["M", "Q", "S", "K", "...
- 28.8k
15
votes
4
answers
69k
views
How to check whether a List<String> contains a specific string?
Here's what I'm trying to do:
I have some List<String>, I want to print a statement if the List contains a particular string, else throw an Exception but when I try the following code
List<...
- 243
15
votes
2
answers
49k
views
Generating a json in a loop in python
I have some difficulties generating a specific JSON object in python.
I need it to be in this format:
[
{"id":0 , "attributeName_1":"value" , "attributeName_2&...
- 7,472
15
votes
3
answers
17k
views
Counting 2d lists in python
How can I count the number of items that are 'hit' in this 2d list??
grid = [['hit','miss','miss','hit','miss'],
['miss','miss','hit','hit','miss'],
['miss','miss','miss','hit','hit'],
...
- 215
15
votes
5
answers
2k
views
Python splitting list to sublists at given start/end keywords
If I were to have a list, say
lst = ['hello', 'foo', 'test', 'world', 'bar', 'idk']
I'd like to split it into a sublist with 'foo' and 'bar' as start and end keywords, so that I would get
lst = ['...
- 265
14
votes
4
answers
21k
views
Python loops with multiple lists? [duplicate]
<edit>
Thanks to everyone who has answered so far. The zip and os.path.join are really helpful. Any suggestions on ways to list the counter in front, without doing something like this:
zip(range(...
agraddy
14
votes
6
answers
23k
views
Why does a for-loop with pop-method (or del statement) not iterate over all list elements [duplicate]
I am new to Python and experimenting with lists
I am using Python 3.2.3 (default, Oct 19 2012, 20:13:42), [GCC 4.6.3] on linux2
Here is my samplecode
>>> l=[1,2,3,4,5,6]
>>> for i ...
- 151