Add column to 2D array in Python

Question

I'm trying to add an extra column to a 2D array in Python but I'm stuck. I have a 2D array like below:

['000', '101']
['001', '010']
['010', '000']
['011', '100']

Then I swap 2 elements from the 2nd column and have something like this:

['000', '101']
['001', '000']
['010', '010']
['011', '100']

I want to take the last column right now and add it as the 3rd one like this:

['000', '101', '101']
['001', '010', '000']
['010', '000', '010']
['011', '100', '100']

But I only managed to get this:

['000', '101']
['001', '000']
['010', '010']
['011', '100']
101
000
010
100

I'm adding a column like this:

col = column(data,1)
data_res += col

I'm creating an array like this:

with open('data.txt', 'r') as f:
     for line in f:
         line_el = line.split()
         data.append(line_el)

I'm swapping like this:

def swap(matrix, id_l, id_r):
    matrix[id_l][1], matrix[id_r][1] = matrix[id_r][1],matrix[id_l][1]
    return matrix

Any ideas?

Are they numpy arrays or lists? Your data is not valid python syntax. — akuiper
– akuiper, Commented Jan 16, 2017 at 21:41

mkrieger1 · Accepted Answer · 2017-01-17 00:50:06Z

5

Since you are writing your 2D list as a list of lists (Row Major Order), adding a column means adding an entry to each row.

It seems you already have some data created like this:

# Create a 2D list
data = [['000', '101'],['001', '010'],['010', '000'],['011', '100']]

So now you could add a new column identical to the last column like this:

# Loop through all the rows
for row in data:
  lastColumn = row[-1]
  # Now add the new column to the current row
  row.append(lastColumn)

edited Jan 17, 2017 at 0:50

mkrieger1

24.2k7 gold badges68 silver badges84 bronze badges

answered Jan 16, 2017 at 21:57

JoshOrndorff

1,72111 silver badges21 bronze badges

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

Comments

GantTheWanderer · Accepted Answer · 2017-01-16 22:00:10Z

0

A list comprehension can do this quickly. This code doesn't perform the swap, but it looks like you have that working already. :)

data = [['000', '101'],['001', '010'],['010', '000'],['011', '100']]
print [x + [x[1]] for x in data]

# [
#     ['000', '101', '101'],
#     ['001', '010', '010'],
#     ['010', '000', '000'],
#     ['011', '100', '100']
# ]

with open('data.txt', 'r') as f:
    for line in f:
        line_el = line.split()
        data.append([x + [x[1]] for x in line_el])

edited Jan 16, 2017 at 22:00

answered Jan 16, 2017 at 21:46

GantTheWanderer

1,2921 gold badge11 silver badges19 bronze badges

Collectives™ on Stack Overflow

Add column to 2D array in Python

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related