Appending specific integers to nested lists - Python

Question

I have a nested list, A = [[1, 2, 3], [5, 2, 7], [4, 8, 9]]. I want to add the numbers 1, 2, 3 in list A to be A = [[1, 2, 3, 1], [5, 2, 7, 2], [4, 8, 9, 3]] and so on (this is just a shorter version). I tried the same using the code I wrote:

i = 0
j = 0
#number_nests = number of nested lists
for i in range(0, number_nests):
    for j in A:
        j.append(i)

print(A)

This is the output which I am getting, since I am a newbie, I am a little stuck: [[1, 90, 150, 0, 1, 2, 3], [2, 100, 200, 0, 1, 2, 3], [4, 105, 145, 0, 1, 2, 3], [3, 110, 190, 0, 1, 2, 3]]. I am trying to do it without numpy.

no need of range(0, number_nests), 0 is default start in range.So simply range(number_nests) — itzMEonTV
– itzMEonTV, Commented May 28, 2015 at 7:13

sachin saxena · Accepted Answer · 2015-05-28 07:09:30Z

3

A = [[1, 2, 3], [5, 2, 7], [4, 8, 9]]
i=1
for val in A:
    val.append(i)
    i += 1

answered May 28, 2015 at 7:09

sachin saxena

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shx2 · Accepted Answer · 2015-05-28 07:09:11Z

3

Simply iterate over the outer list along with the indexes, using enumerate:

for i, elem_list in enumerate(A, start=1):
    elem_list.append(i)

answered May 28, 2015 at 7:09

shx2

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Comments

Tanveer Alam · Accepted Answer · 2015-05-28 07:31:48Z

3

You can use enumerate built-in function with start parameter as 1 to get current index.

A = [[1, 2, 3], [5, 2, 7], [4, 8, 9]]

print([val+[i] for i, val in enumerate(A, 1)])

Using map built-in function

In python 2.x

print map(lambda x,y: x+[y],  A, range(1, len(A)+1))

In python 3.x

print(list(map(lambda x,y: x+[y], A, range(1, len(A)+1))))

edited May 28, 2015 at 7:31

answered May 28, 2015 at 7:09

Tanveer Alam

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Michael Kazarian · Accepted Answer · 2015-05-28 07:14:56Z

1

A = [[1, 2, 3], [5, 2, 7], [4, 8, 9]]
B = [1, 2, 3]
print [A[i]+[B[i]] for i in range(len(A))]
#Output[[1, 2, 3, 1], [5, 2, 7, 2], [4, 8, 9, 3]]

answered May 28, 2015 at 7:14

Michael Kazarian

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Comments

Juh_ · Accepted Answer · 2015-05-28 07:40:56Z

-1

You only need one loop to add one number to each list in A:

for i in range(1, len(A)+1):
    A[i].append(i)

Note: the range should start at 1

edited May 28, 2015 at 7:40

Juh_

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answered May 28, 2015 at 7:13

Youngbin Kim

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