Is there a "pythonic" way of getting only certain values from a list, similar to this perl code:
my ($one,$four,$ten) = line.split(/,/)[1,4,10]
8 Answers
Using a list comprehension
line = '0,1,2,3,4,5,6,7,8,9,10'
lst = line.split(',')
one, four, ten = [lst[i] for i in [1,4,10]]
Comments
I think you are looking for operator.itemgetter:
import operator
line=','.join(map(str,range(11)))
print(line)
# 0,1,2,3,4,5,6,7,8,9,10
alist=line.split(',')
print(alist)
# ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '10']
one,four,ten=operator.itemgetter(1,4,10)(alist)
print(one,four,ten)
# ('1', '4', '10')
3 Comments
Eric Palakovich Carr
Not really. If you take out the demonstrative code it can look like this: one,four,ten=operator.itemgetter(1,4,10)(line.split(','))
Arne Babenhauserheide
You’re a lifesaver, thanks! If timeit is right, this should reduce the runtime of a codesnippet we examined today from 9 hours to a few seconds.
JStrahl
Unnecessary to use a library when it can be achieved with list comprehension, see @has2k1 answer.
lst = line.split(',')
one, four, ten = lst[1], lst[4], lst[10]
4 Comments
Idan K
I think you misunderstood the question
SilentGhost
@Idan: may be I have, am I not supposed to get 2nd, 5th and 11th elements of the new list?
Greg Hewgill
@Idan K: There's no requirement that the "Pythonic" version be a single expression like the Perl version.
Corey Farwell
Although itemgetter might satisfy the OP's request in one line, I have to agree with Lennart here that this solution is most readable and easily understandable
Try operator.itemgetter (available in python 2.4 or newer):
Return a callable object that fetches item from its operand using the operand’s ____getitem____() method. If multiple items are specified, returns a tuple of lookup values.
>>> from operator import itemgetter
>>> line = ','.join(map(str, range(11)))
>>> line
'0,1,2,3,4,5,6,7,8,9,10'
>>> a, b, c = itemgetter(1, 4, 10)(line.split(','))
>>> a, b, c
('1', '4', '10')
Condensed:
>>> # my ($one,$four,$ten) = line.split(/,/)[1,4,10]
>>> from operator import itemgetter
>>> (one, four, ten) = itemgetter(1, 4, 10)(line.split(','))
1 Comment
Arne Babenhauserheide
You’re a lifesaver, thanks! If timeit is right, this should reduce the runtime of a codesnippet we examined today from 9 hours to a few seconds.
How about this:
index = [1, 0, 0, 1, 0]
x = [1, 2, 3, 4, 5]
[i for j, i in enumerate(x) if index[j] == 1]
#[1, 4]
Comments
Yes:
data = line.split(',')
one, four, ten = data[1], data[4], data[10]
You can also use itemgetter, but I prefer the code above, it's clearer, and clarity == good code.
Comments
Alternatively, if you had a Numpy array instead of a list, you could do womething like:
from numpy import array
# Assuming line = "0,1,2,3,4,5,6,7,8,9,10"
line_array = array(line.split(","))
one, four, ten = line_array[[1,4,10]]
The trick here is that you can pass a list (or a Numpy array) as array indices.
EDIT : I first thought it would also work with tuples, but it's a bit more complicated. I suggest to stick with lists or arrays.
Comments
Using pandas:
import pandas as pd
line = "0,1,2,3,4,5,6,7,8,9,10"
line_series = pd.Series(line.split(','))
one, four, ten = line_series[[1,4,10]]
my (...) = (split /,/, $line)[1,4,10];