Using .index() function in nested lists

Question

I am trying to make a program that finds a certain value in a nested list, so I wrote this code:

list = [['S', 'T', 'U', 'T'], ['O', 'P', 'Q', 'R']]

However, when I inputted

list.index('O')

It gave me an error message saying

Traceback (most recent call last):
File "<pyshell#11>", line 1, in <module>
list.index('O')
ValueError: 'O' is not in list

Any ideas?

Very clearly worded. I'm curious the best way to do this too. — efreed
– efreed, Commented Apr 3, 2016 at 3:11

Tonechas · Accepted Answer · 2017-01-07 01:55:35Z

2

Well it is really simple, 'O' is not in the list, it only contains the other lists. Here is an example:

list_you_have = [['S', 'T', 'U', 'T'], ['O', 'P', 'Q', 'R']]
print list_you_have.index(['O','P','Q','R']) #outputs 1

Now if you do it like:

print list_you_have[1].index('O') # it outputs 0 because you're pointing to 
#list which acctualy contains that 'O' char.

Now a function for nested char search would be

def nested_find(list_to_search,char):
    for i, o in enumerate(list_to_search):
        if char in o:
            print "Char %s found at list %s at index %s" % (char, i, o.index(char))

Or maybe an even simpler solution as @zondo commented would be:

def nested_find(list_to_search,char):
    newlist = sum(list_to_search, [])
    if char in newlist:
        print "Char %s is at position %s" % (char, newlist.index(char))

edited Jan 7, 2017 at 1:55

Tonechas

13.8k16 gold badges52 silver badges85 bronze badges

answered Apr 2, 2016 at 23:05

Marko Mackic

2,3431 gold badge12 silver badges19 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

bubble · Accepted Answer · 2016-04-03 00:01:56Z

0

You can solve your problem in one-line:

print item in reduce(lambda x, y: x + y, nestedlists)

answered Apr 3, 2016 at 0:01

bubble

1,6721 gold badge12 silver badges17 bronze badges

1 Comment

zondo Over a year ago

You can use sum(nestedlists, []) instead of that long reduce() call.

Collectives™ on Stack Overflow

Using .index() function in nested lists

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related