replace array elements with elements of a list in NumPy

Question

I have a NumPy array and I converted it into a matrix called string_matrix where each element is a string. Now I want to convert each element in string_matrix to letters. The number in matrix are the index of the list alp. So I want this output : string_matrix = [['l' 'i' 'a']['a' 'f' 'b']['u' 'e' 'k']]

alp = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z",""]
matrix = numpy.array([[11, 8, 0],[0, 5, 1],[20, 4, 10]])
string_matrix = numpy.array(["%.f" % v for v in matrix.reshape(matrix.size)])
string_matrix = string_matrix.reshape(matrix.shape)

Jacques Kvam · Accepted Answer · 2018-11-24 17:59:09Z

1

You can index into the alp list with your matrix, you need to make alp a numpy array first:

numpy.array(alp)[matrix]

Output:

array([['l', 'i', 'a'],
       ['a', 'f', 'b'],
       ['u', 'e', 'k']], dtype='<U1')

This uses numpy's advanced indexing. You can find more details here if you want to read up on it.

edited Nov 24, 2018 at 17:59

answered Nov 24, 2018 at 17:51

Jacques Kvam

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3 Comments

Waterploof Over a year ago

Is it possible to use a loop instead of this numpy's advanced indexing ?

Jacques Kvam Over a year ago

Yea you can loop over the elements of the matrix and index into alp with its individual elements, rows, or columns. What do you want to loop over?

Waterploof Over a year ago

Over its individual elements but I solved this problem, thank you

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