在Python中，如何获取2D数组中“列”的最大值？

Question

In Python how do I get the max value of a 'column' in a 2D array?

I can see that trainingData has a max and min which is the max and min values of the entire 2D array but I would like the max value for each "column".

I've tried several things and this is my last attempt but it didn't seem to work:

creating it:

trainingData = []

filling it:

for row in csv_reader:
    trainingData.append(row)

converting to np

npTrainingData = np.array(trainingData)

printing it:

for x in range(1, 12):
    print(np.max(npTrainingData[:x]))

I've scoured stack overflow but nobody seems to solve this at all but have a ton of similar questions.

Thanks, John

Answer 1

instead of explicitly iterating over the elements (or sub-arrays) of an array like

for x in range(1, 12):
    print(np.max(npTrainingData[:x]))

there are numpy functions, which can be controlled regarding on which axis they are applied. Eg np.max :

np.max(npTrainingData, 0)

or equivalently

npTrainingData.max(0)

where the 0 here is the axis parameter, which can be 0 or 1 for 2D-arrays.
When left blank, the maximum of the flattened array, ie a single value for the whole dataset is returned.