In this example:
sorted_data = [files.data[ind] for ind in sort_inds] May someone please provide an explanation as to how the expression behind the for loop is related or how it is working, thanks.
- 5Read on list compressionkarthikr– karthikr2013-10-17 22:57:31 +00:00Commented Oct 17, 2013 at 22:57
- 6I think @karthikr means list comprehension docs.python.org/2/tutorial/…Stuart– Stuart2013-10-17 23:00:10 +00:00Commented Oct 17, 2013 at 23:00
- Please don't downvote a question just because you already know the answer. I spent quite a while googling for this, merely because I didn't know the name for it. Seeing the expression precede the for-in definitely made me scratch my head, having never seen a list comprehension expressed this way.Ishmael Smyrnow– Ishmael Smyrnow2015-03-01 02:02:44 +00:00Commented Mar 1, 2015 at 2:02
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3 Answers
It's called a List Comprehension
In other words
sorted_data = [files.data[ind] for ind in sort_inds] is equivalent to:
sorted_data = [] for ind in sort_inds: sorted_data.append(files.data[ind]) It's just a lot more readable using the comprehension
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ok so here is a simple example:
say i have a list of ints:
nums = [1,2,3] and i do this:
[i**2 for i in nums] it will output:
[1, 4, 9] this is equivalent to this: for i in nums: list.append(i**2)
because it iterated through the list and squared each item in the list
another example:
say i have a list of strings like this:
list1 = ['hey, jim','hey, pam', 'hey dwight'] and I do this:
[phrase.split(',') for phrase in list1] this will output this list:
[['hey', ' jim'], ['hey', ' pam'], ['hey dwight']] this is equivalent too:
for phrase in list1: new_phrase = phrase.split(',') list.append(new_phrase) it went through and made a list out of each item but it used split on each item
its basically a compacted for loop and instead of using append() it just creates the list!. it is much more readable and takes less lines
learn more here
Comments
It means for every item in this case ind present in sort_inds, pass it as a parameter to the function files.data[ind].
Save the result in a list (sorted_data)
