Changing Values in Row 0 of Numpy Array

Question

I'm having trouble changing the values in a numpy array. I have already set up the array of zeros. Pvfv is present value and future value

pvfv=np.zeros((7,5))
print(pvfv)

Output:

[[ 0.00     0.00     0.00     0.00     0.00]
 [ 0.00     0.00     0.00     0.00     0.00]
 [ 0.00     0.00     0.00     0.00     0.00]
 [ 0.00     0.00     0.00     0.00     0.00]
 [ 0.00     0.00     0.00     0.00     0.00]
 [ 0.00     0.00     0.00     0.00     0.00]
 [ 0.00     0.00     0.00     0.00     0.00]]

Now I want to use np.array change row 0 to look like, keeping the rest of the array constant:

 [[ 0.00     1.00     2.00     3.00     4.00]
  [ 0.00     0.00     0.00     0.00     0.00]
  [ 0.00     .....

pvfv=np.zeros((7,5)); pvfv[0,:] = np.array([i for i in range(pvfv.shape[1])]) — Thierno Amadou Sow
– Thierno Amadou Sow, Commented Apr 23, 2022 at 16:04

Vero · Accepted Answer · 2022-04-23 16:01:51Z

2

Simply use:

import numpy as np

n = 7
p = 5
zeros = np.zeros((n, p))
print("before: \n", zeros, "\n")

row = np.arange(0, p, dtype = float) #no need to copy but just to make things clear.
zeros[0] = row;
print("after: \n", zeros, "\n")

output:

before: 
[[0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]] 

after: 
[[0. 1. 2. 3. 4.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]
 [0. 0. 0. 0. 0.]]

answered Apr 23, 2022 at 16:01

Vero

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2 Comments

NewAtCoding Over a year ago

Thank you for helping me understand. Is adding the dtype =float necessary in all scenarios?

Vero Over a year ago

It doesn't matter in this case as the matrix entries (i.e. row 0) will be casted to the original type of the matrix e.g. numpy.float64.

Daniel · Accepted Answer · 2022-04-23 16:00:16Z

0

You could do the top row and then stack it above the rest:

np.vstack((np.arange(5), np.zeros((6, 5))))

answered Apr 23, 2022 at 16:00

Daniel

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