Modifying lists within lists via list comprehension

Question

how can I get these loops and if statements into a comprehension?

raw = [['-', 'bla'], ['-', 'la'], ['=', 'bla']]

for one in raw:
    if one[0] == '-':
        for two in raw:
            if two[1] == one[1] and two[0] == '=': two[0] = '--'

So far:

[two+one for two in raw for one in raw]

But not sure where to put the if statements:

if one[0] == '-' and if two[1] == one[1] and two[0] == '=': two[0] = '--'

the example code returns raw as [['-', 'bla'], ['-', 'la'], ['--', 'bla']] — Rhys
– Rhys, Commented Mar 19, 2018 at 1:43
I've answered based on your desired output, as your logic is confusing. — jpp
– jpp, Commented Mar 19, 2018 at 1:49

jpp · Accepted Answer · 2018-03-19 02:30:58Z

2

A simple list comprehension should be sufficient:

raw = [['-', 'bla'], ['-', 'la'], ['=', 'bla']]

res = [['--' if (i != '-') and (['-', j] in raw) else i, j] for i, j in raw]

Result:

[['-', 'bla'], ['-', 'la'], ['--', 'bla']]

edited Mar 19, 2018 at 2:30

answered Mar 19, 2018 at 1:48

jpp

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3 Comments

Rhys Over a year ago

I need raw [2]'s '=' value to change to -- only if an iteration of its companion string 'bla' with - exists ..... so the result will be ... if any bla exists with the - ... then all other blas that dont have - will have --

Rhys Over a year ago

thanks for this. Out of curiosity, if i returns ['-', '-', '='] and j returns ['bla', 'la', 'bla'] ... how is every bla asking every other bla (and la) if it has a - value?

Rhys Over a year ago

oh it's the in raw part!

Aaditya Ura · Accepted Answer · 2018-03-19 05:59:02Z

0

You can set item in list comprehension ,

Your code:

for one in raw:
    if one[0] == '-':
        for two in raw:
            if two[1] == one[1] and two[0] == '=': two[0] = '--'

convert to list comprehension :

[[two.__setitem__(0,'--') if two[1]==one[1] and two[0]=='=' else two for two in raw] if one[0]=='-' else one for one in raw]
print(raw)

output:

[['-', 'bla'], ['-', 'la'], ['--', 'bla']]

answered Mar 19, 2018 at 5:59

Aaditya Ura

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