如何从列表中的每个numpy数组中提取最大值？

Question

Actually, i'm very new to python and working on some image problem statement. Stuck in a problem and not able to get out of this.

I have data frame like:

Image                       RGB                 max_1 max_2 max_3
file1   [[224,43,234][22,5,224][234,254,220]]     234   224   254
file2   [[22,143,113][221,124,224][234,254,123]]  143   224   254
file3   [[44,45,2][2,5,4][34,254,220]]             45     5   254
file4   [[224,243,34][22,5,24][24,25,20]]         243    24    25
file5   [[210,13,34][22,5,224][234,254,220]]      210   224   254

I tried np.max() but it gave me unexpected results that means for the first row this gave me output 254 , and so on.

I'm expecting the output as column max_1, max_2, and max_3.

Answer 1

I'll assume that you want the max values of R, G and B respectively. If you want this then, here is one way to do it:

a = np.array([ [224,43,234], [22,5,224], [234,254,220]])
r_max = a.T[0].max()
g_max = a.T[1].max()
b_max = a.T[2].max()

Answer 2

Using list-comprehension :

a = np.array([[224,43,234], [22,5,224], [234,254,220]])

print([x.max() for x in a])

OUTPUT :

[234, 224, 254]

Answer 3

You can do something like this perhaps:

file1 = [[224,43,234],[22,5,224],[234,254,220]]

for idx, inner_list in enumerate(file1):
    print('max_'+str(idx+1)+' : '+str(max(inner_list)))

Answer 4

Another way:

import numpy as np

a=np.array([[1,2,3],[11,12,13],[21,22,23]])
print(a)

maxInRows = np.amax(a, axis=1)
print('Max value of every Row: ', maxInRows)

Answer 5

You said you have a data frame, so I assume it's a pandas DataFrame object. In which case, you can use list comprehension to take the max from each sub-list in the list, and assign each element to a new column (this loop isn't elegant but will work):

df['max_colors'] = df['RGB'].apply(lambda x: [np.max(color) for color in x])
for i in range(3):
    df['max_'+str(i)] = df['max_colors'].apply(lambda x: x[i])

Answer 6

Solved the problem like this. Thanks for having all the answers.

df['max_1'] = 0
df['max_2'] = 0
df['max_3'] = 0
for i in range(5):
    df['max_1'][i] = df['RGB'][i][0].max()
    df['max_2'][i] = df['RGB'][i][1].max()
    df['max_3'][i] = df['RGB'][i][2].max()