convert all rows to columns and columns to rows in Arrays

Question

I'm trying to create this program (in python) that converts all rows to columns and columns to rows.

To be more specific, the first input are 2 numbers. N and M. N - total rows,M total columns. I've used b=map(int, raw_input().split()). and then based on b[0], Each of the next N lines will contain M space separated integers. For example:

Input:

3 5
13 4 8 14 1
9 6 3 7 21
5 12 17 9 3

Now the program will store it in a 2D array:

arr=[[13, 4, 8, 14, 1], [9, 6, 3, 7, 21], [5, 12, 17, 9, 3]]

What's required for the output is to print M lines each containing N space separated integers. For example:

This is what I've tried so far:

 #Getting N and M from input
 NM=map(int, raw_input().split())
 arr=[]

 for i in xrange(NM[0]):
     c=map(int, raw_input().split())
     arr.append(c)

I've created a 2D array and got the values from input but I don't know the rest. Let me make this clear that I'm definitely NOT asking for code. Just exactly what to do to convert rows to columns and in reverse.

Thanks in advance!

score 7 · Accepted Answer · answered Sep 06 '16 at 12:04

7

You can use zip to transpose the data:

arr = [[13, 4, 8, 14, 1], [9, 6, 3, 7, 21], [5, 12, 17, 9, 3]]
new_arr = zip(*arr)
# [(13, 9, 5), (4, 6, 12), (8, 3, 17), (14, 7, 9), (1, 21, 3)]

answered Sep 06 '16 at 12:04

Jon Clements

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Thank you so much! Is there any other way to do it not using built-in functions? – marc_s Sep 06 '16 at 12:08
1

`for j in range(len(arr[0])): print(" ".join(str(i[j]) for i in arr))` will print exactly what you want – Jean-François Fabre Sep 06 '16 at 12:10
@RUser98 Why would you not wanna use built-ins? The traditional way is to loop through, But hey, If you wanna re-invent the wheel, you might just end up with a flat tyre! – Bhargav Rao Sep 06 '16 at 12:10
it returns a list of tuples not a list of lists – Oct 02 '20 at 09:10

convert all rows to columns and columns to rows in Arrays

1 Answers1