NumPy: remove element from a 3-dimensional array

Question

I have a 2-dimensional array with each element being a list of valid values (pseudosyntax):

[ [1,2] [1,2]
  [1,2] [1,2] ]

so effectively it's a 3-dim array/list/matrix (whatever Python calls those.)

It is generated by

    import numpy as np
    grid = np.full((borderSize, borderSize, borderSize), range(1, borderSize + 1))

What is the best practice to remove a value from an array on the "deepest" level?

Pseudocode:

grid = [ [1,2] [1,2]
  [1,2] [1,2] ]

grid[0,1].remove(not index but value 2)

#result: grid = [ [1,2] [1]
                  [1,2] [1,2] ]

I did attempt every solution I could google, including numpy.delete() and array.remove(), any whatever that syntax is: arr = arr[ (arr >= 6) & (arr <= 10) ]. All the approaches seem to "flatten" the array/list/matrix, or throw cryptic-to-me errors ("can't broadcast array into shape")

Thanks!

Marcin · Accepted Answer · 2020-11-01 12:27:52Z

1

Arrays don't really have such a thing as a "deepest" level, they have dimensions and each and every dimension has to be defined globally. You can change your array to a list and then remove the element like that:

grid = np.array([ [1,2], [1,2],
  [1,2], [1,2] ])

grid = grid.tolist()

del grid[1][1]

grid

result:

[[1, 2], [1], [1, 2], [1, 2]]

but you cannot do this on an array.

answered Nov 1, 2020 at 12:27

Marcin

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2 Comments

Zsolt Szilagyi Over a year ago

Thanks! Quick sanity check: I can't convert that list back to array, as not each "member" has the same number of elements - correct?

Marcin Over a year ago

yup, arrays have to have dimensions defined. you can see your array dimension by typing grid.shape

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