如何将字符串列表中的元素添加到python中的数组

Question

I have a list of strings that look like this, and I need to add the first, second, and third entry of each to a integer list ab and c accordingly

print cuts gives me

[['3', '5', '10'], ['2', '8', '15'], ['7', '9', '25'], ['4', '6', '20'], ['9', '12', '50'], ['5', '7', '22'], ['3', '8', '17'], ['6', '9', '24'], ['8', '11', '40'], ['7', '10', '30'], []]

such that a = [3,2,7, ... , 7] b = [5, 8, 9, ... , 10] c = [10, 15, ... , 30]

(Also want these to be ints not strings)

I tried to delimit by

cuts[i] = cuts[i].strip(",")

thinking that it would give me [[3] [5] [10] ] which would let me add with a for loop but python told me lists don't have a strip attribute

Answer 1

Here are list comprehensions in basic form:

data = [['3', '5', '10'], ['2', '8', '15'], ['7', '9', '25'], ['4', '6', '20'],
        ['9', '12', '50'], ['5', '7', '22'], ['3', '8', '17'], ['6', '9', '24'],
        ['8', '11', '40'], ['7', '10', '30'], []]

a = [int(x[0]) for x in data if len(x) >= 1]
b = [int(x[1]) for x in data if len(x) >= 2]
c = [int(x[2]) for x in data if len(x) >= 3]

print a
print b
print c

Or, to keep them in a 2-dimensional list:

abc = [[int(x[i]) for x in data if len(x) >= i+1] for i in range(len(data[0]))]
print abc

Output:

[[3, 2, 7, 4, 9, 5, 3, 6, 8, 7], 
 [5, 8, 9, 6, 12, 7, 8, 9, 11, 10], 
 [10, 15, 25, 20, 50, 22, 17, 24, 40, 30]]

Answer 2

This can be done using the built in zip function.

a, b, c = zip(*cuts)

You can read about zip here . The gist is here -

this function returns a list of tuples, where the i-th tuple contains the i-th element from each of the argument sequences or iterables

If you then want your lists to hold numbers instead of strings, you can map them over the int function.

a = map(int, a)
b = map(int, b)
c = map(int, c)

Answer 3

I'm assuming that the empty list at the end of cuts is a typo -- otherwise your requirements don't quite make sense since there isn't a first, second and third element of an empty list. You could always use

cuts = [cut for cut in cuts if len(cut) > 0]

if you want to cut cuts down to size.

In any event, once that empty list is removed, what you are asking for is a sort of zip and can be done like thus:

>>> cuts = [['3', '5', '10'], ['2', '8', '15'], ['7', '9', '25'], ['4', '6', '20'], ['9', '12', '50'], ['5', '7', '22'], ['3', '8', '17'], ['6', '9', '24'], ['8', '11', '40'], ['7', '10', '30']]
>>> a,b,c = ([int(s) for s in strings] for strings in zip(*cuts))
>>> a
[3, 2, 7, 4, 9, 5, 3, 6, 8, 7]
>>> b
[5, 8, 9, 6, 12, 7, 8, 9, 11, 10]
>>> c
[10, 15, 25, 20, 50, 22, 17, 24, 40, 30]