CODEWITHSUNDEEP
pythonarrayslistnumpylist-comprehension
Rivered
Rivered

Reputation: 789

How to add numbers to an array except if the number in the array matches a certain value

I want to add a certain number to values of my arrays, with a maximum capping out at 255, but only in cases where the number in the array does not match 0.

Imagine the value I want to add to each number in my array is 20, except if number is 0

#The array to which I want to add a number based on value:
v=array([0,0,0,0,117,119,120,121,16,1,16,10,245,0,0,0,4,5])

value=20
lim = 255 - value 
v[v > lim] = 255
v[v <= lim] += value

#Results in the following array
array([20,20,20,20,137,139,140,141,36,21,36,30,255,20,20,20,24,25])

This works, but also adds when the number is 0. However, I want to have a statement in there, that adds 20 in all cases, except if the number in the array is 0! Expected outcome:

array([0,0,0,0,137,139,140,141,36,21,36,30,255,0,0,0,24,25])

Wasn't able to find a good solution or figure out how.

Upvotes: 0

Views: 125

Answers (3)

Hamza usman ghani
Hamza usman ghani

Reputation: 2243

Use these two lines to achieve your expected output

  • add 20 to all non zero values v[(v!=0)] += 20
  • cap out values to 255 v[v > 255] = 255

Complete Code:

v= np.array([0,0,0,0,117,119,120,121,16,1,16,10,245,0,0,0,4,5])
value=20
lim = 255
v[v!=0] += value
v[v>lim] = lim
print(v)

>> [  0   0   0   0 137 139 140 141  36  21  36  30 255   0   0   0  24  25]

Upvotes: 1

Daweo
Daweo

Reputation: 36340

I would do it following way:

import numpy as np
v = np.array([0,0,0,0,117,119,120,121,16,1,16,10,245,0,0,0,4,5])
value = 20
lim = 255
v += (v!=0)*value
v = np.clip(v, None, lim)
print(list(v))

output

[0, 0, 0, 0, 137, 139, 140, 141, 36, 21, 36, 30, 255, 0, 0, 0, 24, 25]

Explanation: I treat boolean array of where there are non-zero as array of 0s and 1s, thus by multiplying by value I get value to add for each element, then I use numpy.clip to replace values beyond lim.

Upvotes: 1

Mike Jack
Mike Jack

Reputation: 170

Replace v[v <= lim] += value with v[(v != 0) & (v <= lim)] += value

Upvotes: 1

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