Appending an Array at a specific Index in Python

Question

I have an array like this.

    [['Bob\n', 0], ['Joe\n', 0], ['Bill', 0], ['Steve', 0], ['Judy', 0]]

and I would like to change one of the zeros to 1. How would I direct a .append to the 0 after Joe for example. I am new to python and can not currently use numPy unfortunately. Also how do you get rid of that stupid \n at the end of a few of the lists?

change and append have different meaning. You want to change the value or append the new value? — Moinuddin Quadri
– Moinuddin Quadri, Commented Dec 16, 2016 at 19:49

Zulu · Accepted Answer · 2016-12-16 19:56:43Z

2

You can use list indexes:

>>> mylist = [['Bob\n', 0], ['Joe\n', 0], ['Bill', 0], ['Steve', 0], ['Judy', 0]]
>>> mylist[1][1] = 'new_value'
>>> mylist
[['Bob\n', 0], ['Joe\n', 'new_value'], ['Bill', 0], ['Steve', 0], ['Judy', 0]]

In mylist, in 2nd element (1), in 2nd element of sublist, I set 'new_value'

And for \n, you can use str.strip:

>>> mylist = [['Bob\n', 0], ['Joe\n', 0], ['Bill', 0], ['Steve', 0], ['Judy', 0]]
>>> mylist = [[i.strip(), j] for i, j in mylist]
>>> mylist
[['Bob', 0], ['Joe', 0], ['Bill', 0], ['Steve', 0], ['Judy', 0]]

Use a list-comprehension and apply strip to 1st element of all sublists.

edited Dec 16, 2016 at 19:56

answered Dec 16, 2016 at 19:51

Zulu

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1 Comment

Moses Koledoye Over a year ago

Change the zero to one, not append a new zero. OP is not very clear tho.

appills · Accepted Answer · 2016-12-16 20:05:10Z

it wont let me comment, but I wanted to add to zulu's answers:

>>>mylist = [['Bob\n', 0], ['Joe\n', 0], ['Bill', 0], ['Steve', 0], ['Judy', 0]]
#so far so good, but change mylist[1][0] to mylist[1][1]
>>>mylist[1][1] = 1
>>>mylist
[['Bob\n', 0], ['Joe\n', 1], ['Bill', 0], ['Steve', 0], ['Judy', 0]]

you can access an element of a list using [int] so, mylist[1] is the element of mylist. mylist[1] also happens to be a list. lets say this (assume I didnt change the value yet):

>>>inside_list = mylist[1]
>>>inside_list
['Joe\n', 0]

now I can access this inside list. 0 is the number i want to replace, at index 1, so we can do this:

>>>inside_list[1] = 1
>>>inside_list
['Joe\n', 1]

as a side note, since 0 is an integer, you can also do this:

>>>inside_list[1]+=1
>>>inside_list
['Joe\n', 1]

DaveQ · Accepted Answer · 2016-12-16 20:12:12Z

0

>>>input = [['Bob\n', 0], ['Joe\n', 0], ['Bill', 0], ['Steve', 0], ['Judy', 0]] >>>output = map(lambda x: [x[0].rstrip(), x[1] or 1], input)

>>>output

>>>[['Bob', 1], ['Joe', 1], ['Bill', 1], ['Steve', 1], ['Judy', 1]]

answered Dec 16, 2016 at 20:12

DaveQ

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