The output always has the same dimensionality as the input, and the individual axes are affected as follows:
The axes specified in the 'axes' parameter have their length reduced to 1 (by applying the reducer).
If the reducer has multiple inputs or multiple outputs, the axis specified in 'fieldAxis' will be used to provide the reducer's inputs and store the reducer's outputs.
All other axes are unaffected (independent reductions are performed).
Usage Returns Array.reduce(reducer, axes, fieldAxis)
Array Argument Type Details this: array
Array The array. reducer
Reducer The reducer to apply. Each of its outputs must be a number, not an array or other type. axes
List The list of axes over which to reduce. The output will have a length of 1 in all these axes. fieldAxis
Integer, default: null The axis to use as the reducer's input and output fields. Only required if the reducer has multiple inputs or multiple outputs, in which case the axis must have length equal to the number of reducer inputs, and in the result it will have length equal to the number of reducer outputs.