ak.layout.IndexedArray — Awkward Array documentation

# ak.layout.IndexedArray

The IndexedArray concept is implemented in 3 specialized classes:

> - `ak.layout.IndexArray64`: `index` values are 64-bit signed integers.

> - `ak.layout.IndexArray32`: `index` values are 32-bit signed integers.

> - `ak.layout.IndexArrayU32`: `index` values are 32-bit unsigned integers.

The IndexedArray class is a general-purpose tool for changing the order of and/or duplicating some `content`. Its `index` array is a lazily applied np.take (integer-array slice, also known as “advanced indexing”).

It has many uses:

> - representing a lazily applied slice.

> - simulating pointers into another collection.

> - emulating the dictionary encoding of Apache Arrow and Parquet.

IndexedArray doesn’t have a direct equivalent in Apache Arrow.

Below is a simplified implementation of a IndexedArray class in pure Python that exhaustively checks validity in its constructor (see ak.is_valid) and can generate random valid arrays. The `random_number()` function returns a random float and the `random_length(minlen)` function returns a random int that is at least `minlen`. The `RawArray` class represents simple, one-dimensional data.

    class IndexedArray(Content):
        def __init__(self, index, content):
            assert isinstance(index, list)
            assert isinstance(content, Content)
            for x in index:
                assert isinstance(x, int)
                assert 0 <= x < len(content)   # index[i] must not be negative
            self.index = index
            self.content = content

        @staticmethod
        def random(minlen, choices):
            if minlen == 0:
                content = random.choice(choices).random(0, choices)
            else:
                content = random.choice(choices).random(1, choices)
            if len(content) == 0:
                index = []
            else:
                index = [random.randint(0, len(content) - 1)
                             for i in range(random_length(minlen))]
            return IndexedArray(index, content)

        def __len__(self):
            return len(self.index)

        def __getitem__(self, where):
            if isinstance(where, int):
                assert 0 <= where < len(self)
                return self.content[self.index[where]]
            elif isinstance(where, slice) and where.step is None:
                return IndexedArray(self.index[where.start:where.stop], self.content)
            elif isinstance(where, str):
                return IndexedArray(self.index, self.content[where])
            else:
                raise AssertionError(where)

        def __repr__(self):
            return "IndexedArray(" + repr(self.index) + ", " + repr(self.content) + ")"

        def xml(self, indent="", pre="", post=""):
            out = indent + pre + "<IndexedArray>\n"
            out += indent + "    <index>" + " ".join(str(x) for x in self.index) + "</index>\n"
            out += self.content.xml(indent + "    ", "<content>", "</content>\n")
            out += indent + "</IndexedArray>\n"
            return out

Here is an example:

    IndexedArray([3, 5, 1, 1, 5, 3],
                 RawArray([8.9, 3.2, 5.4, 9.8, 7.5, 1.9]))

    <IndexedArray>
        <index>3 5 1 1 5 3</index>
        <content><RawArray>
            <ptr>8.9 3.2 5.4 9.8 7.5 1.9</ptr>
        </RawArray></content>
    </IndexedArray>

which represents the following logical data.

    [9.8, 1.9, 3.2, 3.2, 1.9, 9.8]

In addition to the properties and methods described in ak.layout.Content, an IndexedArray has the following.

## ak.layout.IndexedArray.__init__

ak.layout.IndexedArray.__init__(index, content, identities=None, parameters=None)

## ak.layout.IndexedArray.index

ak.layout.IndexedArray.index

## ak.layout.IndexedArray.content

ak.layout.IndexedArray.content

## ak.layout.IndexedArray.isoption

ak.layout.IndexedArray.isoption

Returns False because this is not an IndexedOptionArray.

## ak.layout.IndexedArray.project

ak.layout.IndexedArray.project(mask=None)

Returns an array with the `index` applied to reorder/duplicate elements.

If `mask` is a signed 8-bit ak.layout.Index in which `0` means valid and `1` means missing, only valid elements according to this `mask` are returned.

## ak.layout.IndexedArray.bytemask

ak.layout.IndexedArray.bytemask()

Returns an 8-bit signed ak.layout.Index of all zeros, because this IndexedArray does not have ak.types.OptionType.

## ak.layout.IndexedArray.simplify

ak.layout.IndexedArray.simplify()

Combines this node with its `content` if the `content` also has ak.types.OptionType or is an ak.layout.IndexedArray; otherwise, this is a pass-through. In all cases, the output has the same logical meaning as the input.

This method only operates one level deep.