CODEWITHSUNDEEP
pythonarraysnumpy
user3357979
user3357979

Reputation: 627

Rearrange row elements using numpy in Python

I'm very new to python so i would appreciate any help I can get. How can I rearrange A to look like B?

A=([3,5,6,9,0,0,0,0,0])
B=([0,0,3,0,5,6,0,0,9])

Specifically, I want to rearrange A using the the entries as an index. So I want the 3rd, 5th, 6th, and 9th elements of B to be the value of that index.

Upvotes: 0

Views: 182

Answers (2)

ysakamoto
ysakamoto

Reputation: 2532

I assume that you don't have any duplicate element in A or the element that is larger than the length of the list A. Then, using list comprehension,

B = [ i if i in A else 0 for i in range(1,10) ]

would work.

Explanation:

First, a list comprehension

[i for i in range(1,10)]

gives [1, 2, 3, 4, 5, 6, 7, 8, 9]. You want to put 0 if an element in this list does not belong to the list A. Thus, you replace the first i in the list comprehension to i if i in A else 0. It means that i is left alone if it belongs to A, orelse substitute 0.

Upvotes: 2

Andy Hayden
Andy Hayden

Reputation: 375535

Since this is tagged numpy, here's a numpy solution:

In [11]: A = np.array([3,5,6,9,0,0,0,0,0])

Extract the poisition of the nonzero elements in A:

In [12]: np.nonzero(A)[0]
Out[12]: array([0, 1, 2, 3])

In [13]: ind = A[np.nonzero(A)[0]]

Trimming the zeroes may be equivalent (depending on the rules of the game):

In [14]: np.trim_zeros(A)
Out[14]: array([3, 5, 6, 9])

Create a B of zeroes and then fill with ind:

In [15]: B = np.zeros(A.max() + 1)

In [16]: B[ind] = ind

In [17]: B
Out[17]: array([ 0.,  0.,  0.,  3.,  0.,  5.,  6.,  0.,  0.,  9.])

Upvotes: 4

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