CODEWITHSUNDEEP
pythonarrays
Pazu
Pazu

Reputation: 287

Shifting columns of an array to the left

My goal is to shift the columns of an array B k positions to the left. Assume B is of the shape (n,n). Then of course, the columns from n to n-k have to replaced with some new entries. But this shouldn't be of importance here. What does work is the following:

for i in range(n):
   for j in range(n-k):
      B[i][j]  = B[i][j+k]

I wonder if there is a faster and simpler method. Any suggestions appreciated

Upvotes: 1

Views: 53

Answers (2)

Alain T.
Alain T.

Reputation: 42143

You could use subscripts:

B = B[k:] + newValues

or, if you want to keep the array size and manipulate the original positions afterward:

B[:k] = B[k:2*k]

note that, in this last approach, you must have 2k <= n otherwise you won't have enough elements to fill the left side of the array

Upvotes: 0

log0
log0

Reputation: 10917

If you were using your matrix in column-major order (i.e. using i as column index), much less copies would be needed

for j in range(n-k):
   B[i] = B[i+k]

in this case only the reference to the column is copied

Upvotes: 1

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