& operation for Nd4J

Is there a way to implement the & or &= for nd4j arrays?

for example I want to find relative extrema so I wrote the following function:

    private static INDArray boolrelextrema(
        INDArray data, BiFunction<INDArray, INDArray, INDArray> comp, int order) {

        if (order < 1) {
            throw new IllegalArgumentException("Order must be >= 1");
        if (data.isMatrix()) {
            throw new IllegalArgumentException("Argrelextrema currently only supports 1-D arrays");

        long length = data.length();
        INDArray locs = Nd4j.createFromArray(IntStream.range(0, (int) length).toArray());
        int[] shifts = IntStream.range(1, order + 1).toArray();

        INDArray results = Nd4j.ones(DataType.BOOL, length);
        for (int shift : shifts) {
            // same as np.take(locs + shift, axis=0, mode='clip')
            INDArray plus = data.get(NDArrayIndex.interval(shift, length));
            plus = Nd4j.concat(0, plus, data.get(NDArrayIndex.point(length - 1)));

            // same as np.take(locs - shift, axis=0, mode='clip')
            INDArray minus = data.get(NDArrayIndex.interval(0, length - shift));
            minus = Nd4j.concat(0, data.get(NDArrayIndex.point(0)), minus);

            // find relative peaks
            results = results
                 .eq(comp.apply(data, plus))
                 .eq(comp.apply(data, minus));
            if (!results.any()) {
                return results;
        return results;

but instead of .eq(), what I need in the results calculation is

results &= comp.apply(data, plus)
results &= comp.apply(data, minus)

or perhaps

   results = results
        .and(comp.apply(data, plus))
        .and(comp.apply(data, minus))

I can think of some workarounds, but I was hoping to be missing some native nd4j operation that would allow this. Thanks in advance!

I guess you are looking for something like this?

You can access it from Nd4j.math.and.

It is using the And Op, so in principle you can create your own “in-place and” by passing the target (z) when instantiating the op.

Thank you for the quick response. That’s what I was looking for.

“and” was just too common a keyword to find it via a google search, and I’m not yet fluent at where to look in the javadoc for certain categories of operations. Thank you again.

A pretty good place to start looking for this kinds of things is here:

Not all ops are mapped there, but most are, and they have a bit of documentation attached to them.

If you can’t find something there, you can press the t button to bring up Github’s file search and search for class names. In this case searching for “and.java” this way brings up a few things :slight_smile:

1 Like

Hey, that is a very neat trick! Sure enough I see a bunch of stuff. Thanks!