how to combine 2D arrays into a 3D array in python?

Question

I have a project in which there is a for loop running about 14 times. In every iteration, a 2D array is created with this shape (4,3). I would like to concatenate those 2D arrays into one 3D array (with the shape of 4,3,14) so that every 2D array would be in different "layer". How should that be implemented in Python?

Answer 1

You can use numpy.dstack() to turn a list of 2D arrays into a 3D array:

https://docs.scipy.org/doc/numpy/reference/generated/numpy.dstack.html

Answer 2

If your array sizes are static as you mentioned, you can do the following

output_array = numpy.zeros((14,4,3), dtype=np.float32)
for i in range(14):
    mat = numpy.random.rand(4,3)
    output_array[i] = mat

you initialize your final array to the size you want and then loop over and assign your matrix (4,3) to the index of that respective loop counter.

The shape and your final matrix is

numpy.shape(output_array)

returns you

(14, 4, 3)

Output is

array([[[ 0.62507486,  0.3246161 ,  0.43934602],
    [ 0.14476213,  0.76139957,  0.92813474],
    [ 0.26556504,  0.02475475,  0.90740073],
    [ 0.08017973,  0.97526789,  0.2213122 ]],

   [[ 0.70042586,  0.8122381 ,  0.79289031],
    [ 0.0369414 ,  0.10780825,  0.77501732],
    [ 0.10386232,  0.86237574,  0.5829311 ],
    [ 0.1888348 ,  0.85105735,  0.31599012]],

   [[ 0.26350111,  0.8787083 ,  0.12869285],
    [ 0.25927794,  0.25701383,  0.81212741],
    [ 0.06661031,  0.53449911,  0.50212061],
    [ 0.40009728,  0.78002244,  0.81524432]],

   [[ 0.49921468,  0.82028496,  0.51261139],
    [ 0.62790054,  0.64566481,  0.02624587],
    [ 0.39364958,  0.99537313,  0.33225098],
    [ 0.88214922,  0.20252077,  0.78350848]],

   [[ 0.29032609,  0.95975012,  0.06733917],
    [ 0.24497923,  0.51818371,  0.93520784],
    [ 0.80267638,  0.88271469,  0.30779642],
    [ 0.57030594,  0.34175804,  0.52563131]],

   [[ 0.61039209,  0.57186425,  0.76554799],
    [ 0.55681604,  0.33107477,  0.05680386],
    [ 0.15465826,  0.13452645,  0.09498007],
    [ 0.29682869,  0.93196124,  0.94435322]],

   [[ 0.23904459,  0.94893754,  0.97033942],
    [ 0.89159942,  0.85306913,  0.02144577],
    [ 0.57696968,  0.82578647,  0.33358794],
    [ 0.81979036,  0.73351973,  0.027876  ]],

   [[ 0.6568135 ,  0.25458351,  0.10369358],
    [ 0.06151289,  0.00939822,  0.00798484],
    [ 0.92518032,  0.19057493,  0.84838325],
    [ 0.78189474,  0.15273546,  0.34607282]],

   [[ 0.46961641,  0.19778872,  0.1498462 ],
    [ 0.55704814,  0.96889585,  0.08894933],
    [ 0.48003736,  0.59383452,  0.42212519],
    [ 0.78752649,  0.07204869,  0.4215464 ]],

   [[ 0.6454156 ,  0.84189773,  0.10041234],
    [ 0.89345407,  0.60821944,  0.56667495],
    [ 0.62806529,  0.67642623,  0.4951494 ],
    [ 0.85371262,  0.13159418,  0.3402876 ]],

   [[ 0.39828625,  0.50659049,  0.34835485],
    [ 0.06839356,  0.74652916,  0.5722388 ],
    [ 0.20762053,  0.0692997 ,  0.02790474],
    [ 0.84786427,  0.98461425,  0.19105092]],

   [[ 0.36976317,  0.44268745,  0.23061621],
    [ 0.47827819,  0.43044546,  0.90150601],
    [ 0.2307732 ,  0.61590552,  0.82066673],
    [ 0.49611789,  0.4480612 ,  0.46685895]],

   [[ 0.40907925,  0.15996945,  0.05480348],
    [ 0.70230347,  0.00926704,  0.97775948],
    [ 0.19834276,  0.20127937,  0.44351548],
    [ 0.48512974,  0.07319999,  0.5580616 ]],

   [[ 0.35749629,  0.88443983,  0.55465496],
    [ 0.61600298,  0.08260803,  0.4010818 ],
    [ 0.40910226,  0.31984288,  0.50188118],
    [ 0.34836289,  0.14394118,  0.06841569]]], dtype=float32)

Hope that helps