Python merge two arrays based on specific value

Question

I have two arrays

array1 = [[ 37.06853867  30.22016525  24.13002205  23.74543762  28.23823929
   29.85162544]
 [ 36.39044189  27.74254036  20.38976479  21.59453011  30.35881233
   34.24060822]
 [ 34.39845657  26.73529243  22.30514145  27.13420486  38.91122437
   48.05885315]
 [ 38.22272491  40.40032578  43.52813721  47.13837051  54.32110977
   64.78022003]
 [ 47.3240242   57.3037529   62.097332    62.22722626  62.09951782
   64.59619141]
 [ 29.9451561   37.32279587  41.77493668  45.76233673  49.91016388
   53.55546951]]


array2 = [[255 255 255 255 255 255]
 [255 255   1 1 255 255]
 [255 255 255 1 255 255]
 [255 255 255 255 255 255]
 [255 255 255 255 255 255]
 [255 255 255 255 255 255]]

I want to add them together. But I only want to add values from array2 to array1 if the value is not 255. How can I do this?

are they the same shape?

Joran Beasley
– Joran Beasley

2013-11-26 00:29:57 +00:00
Commented Nov 26, 2013 at 0:29 — Joran Beasley
– Joran Beasley, Commented Nov 26, 2013 at 0:29
yes, they are the same shape

ustroetz
– ustroetz

2013-11-26 00:30:35 +00:00
Commented Nov 26, 2013 at 0:30 — ustroetz
– ustroetz, Commented Nov 26, 2013 at 0:30

unutbu · Accepted Answer · 2013-11-26 11:31:31Z

3

Here is a way to do it without changing the value of array1 or array2:

mask = (array2 != 255)
result = array1.copy()
result[mask] += array2[mask]
print(result)

edited Nov 26, 2013 at 11:31

answered Nov 26, 2013 at 0:38

unutbu

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Hammer · Accepted Answer · 2013-11-26 00:30:34Z

1

in numpy

#convert to numpy if necessary 
array2 = np.array(array2)
array1 = np.array(array1)

#then it is easy
array2[array2 == 255] = 0
array1 += array2

answered Nov 26, 2013 at 0:30

Hammer

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Comments

Pyrce · Accepted Answer · 2013-11-26 00:40:27Z

1

If you're not using numpy you can do it fairly quickly with zip in a rather large nested list compression call.

[[c1 if c2 == 255 else c1 + c2 for c1, c2 in zip(row1, row2)] 
      for row1, row2 in zip(array1, array2)]

answered Nov 26, 2013 at 0:40

Pyrce

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