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I have a list of lists, and would like to use list comprehension to apply a function to each element in the list of lists, but when I do this, I end up with one long list rather than my list of lists.
So, I have
x = [[1,2,3],[4,5,6],[7,8,9]]
[number+1 for group in x for number in group]
[2, 3, 4, 5, 6, 7, 8, 9, 10]
But I want to get
[[2, 3, 4], [5, 6, 7], [8, 9, 10]]
How do I go about doing this?
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To flatten a list of lists, use the list comprehension statement [x for l in lst for x in l] . To modify all elements in a list of lists (e.g., increment them by one), use a list comprehension of list comprehensions [[x+1 for x in l] for l in lst] .
As it turns out, you can nest list comprehensions within another list comprehension to further reduce your code and make it easier to read still. As a matter of fact, there's no limit to the number of comprehensions you can nest within each other, which makes it possible to write very complex code in a single line.
Difference between list comprehension and for loop. The for loop is a common way to iterate through a list. List comprehension, on the other hand, is a more efficient way to iterate through a list because it requires fewer lines of code.
List comprehensions are used for creating new lists from other iterables. As list comprehensions return lists, they consist of brackets containing the expression, which is executed for each element along with the for loop to iterate over each element.
Use this:
[[number+1 for number in group] for group in x] Or use this if you know map:
[map(lambda x:x+1 ,group) for group in x] Starting from the structure of your data:
x = [[1,2,3],[4,5,6],[7,8,9]]
Every group is a triplet [a,b,c], so I consider for readability a solution like:
«take every group [a,b,c] from the list and provide me the list of [a+1,b+1,c+1] »
x_increased = [ [a+1,b+1,c+1] for [a,b,c] in x ]
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