CODEWITHSUNDEEP
pythonlistnested
Billy Whales
Billy Whales

Reputation: 103

Appending certain elements from a list of list into another list

I have a nested list as shown below:

L = [['James', 'Bob', '23', '47'], ['Earl', 'Carl', '16', '43'], ['Milly', 'Wendy', '1', '21']]

I want to take the names from each of them and put them into a new list called 'newList' without the numbers.

I tried the following code:

for i in L[0][0]:
    newList.append(i)
print(newList)

However, this just printed the first name and each letter was seperated by a comma. I want the new list to look like this: 

newList = ['James', 'Bob', 'Earl', 'Carl', 'Milly', 'Wendy']

Upvotes: 2

Views: 1146

Answers (7)

itzMEonTV
itzMEonTV

Reputation: 20369

You need to iterate over elements in list L

for i in L:
    newList.append(i[0])
    newList.append(i[1])
    #or simply newList.extend(i[:2])
print(newList)

EDIT

for i in L:
    if i[0] not in newList:
        newList.append(i[0])
    if i[1] not in newList:
        newList.append(i[1])
    #or simply newList.extend(i[:2])
print(newList)

Upvotes: 1

elena
elena

Reputation: 4198

Use the isdigit method to see if a str is a digit:

[j for l in L for j in l if not j.isdigit()]

Output:

['James', 'Bob', 'Earl', 'Carl', 'Milly', 'Wendy']

Upvotes: 0

Allen Qin
Allen Qin

Reputation: 19957

Using numpy to slice the list and flatten the results to a 1D list:

import numpy as np
np.array(L)[:,0:2].flatten().tolist()
Out[349]: ['James', 'Bob', 'Earl', 'Carl', 'Milly', 'Wendy']

Upvotes: 0

timgeb
timgeb

Reputation: 78780

Do it in two steps.

First, grab the first two elements of each list:

>>> names_nested = [sub[:2] for sub in L]
>>> names_nested
[['James', 'Bob'], ['Earl', 'Carl'], ['Milly', 'Wendy']]

Then unnest this list:

>>> names = [name for sub in names_nested for name in sub]
>>> names
['James', 'Bob', 'Earl', 'Carl', 'Milly', 'Wendy']

... or do it more comfortably with itertools.chain:

>>> from itertools import chain
>>> list(chain(*(sub[:2] for sub in L)))
['James', 'Bob', 'Earl', 'Carl', 'Milly', 'Wendy']

... or itertools.chain.from_iterable to get rid of the unpacking star and one set of parentheses.

>>> list(chain.from_iterable(sub[:2] for sub in L))
['James', 'Bob', 'Earl', 'Carl', 'Milly', 'Wendy']

Upvotes: 1

akash karothiya
akash karothiya

Reputation: 5950

You can use isdigit() to filter out names

res = [j for i in L for j in i if not j.isdigit()]
['James', 'Bob', 'Earl', 'Carl', 'Milly', 'Wendy']

Upvotes: 1

Reut Sharabani
Reut Sharabani

Reputation: 31339

If the problem is simply the first two elements from each sublist you can do:

from itertools import chain
result = chain.from_iterable(sublist[:2] for sublist in L)

This will produce a chain object, you can use list to evaluate it:

list(result)
# ['James', 'Bob', 'Earl', 'Carl', 'Milly', 'Wendy']

Upvotes: 0

Kasravnd
Kasravnd

Reputation: 107347

Just use a nested list comprehension:

In [61]: [i for sub in L for i in sub[:2]]
Out[61]: ['James', 'Bob', 'Earl', 'Carl', 'Milly', 'Wendy']

Upvotes: 3

Related Questions