How to perform an outer product with custom function (pandas/numpy)?

Issue

This Content is from Stack Overflow. Question asked by P i

My dataframe has N rows.
I have M centroids. Each centroid is the same shape as a dataframe-row.

I need to create a Nrows by Mcols matrix, where the m-th column is created by applying the m-th centroid to the dataframe.

My solution involves pre-creating the output matrix and filling it one column at a time as we manually iterate over centroids.

It feels clumsy. But I can’t see clearly how to do it ‘properly’.

    def getDistanceMatrix(df, centroids):
        distanceMatrix = np.zeros((len(df), len(centroids)))

        distFunc = lambda centroid, row: sum(centroid != row)

        iCentroid = 0
        for _, centroid in centroids.iterrows():
            distanceMatrix[:, iCentroid] = df.apply(
                lambda row: distFunc(centroid, row),
                axis=1
            )
            iCentroid += 1

        return distanceMatrix

    distanceMatrix = getDistanceMatrix(df, centroids)

It feels like some kind of outer-product-with-a-custom-function.

What’s a good way to write this?



Solution

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