ak.copy

Defined in awkward.operations.structure on line 18.

ak.copy(array)

Returns a deep copy of the array (no memory shared with original).

This is identical to np.copy and copy.deepcopy.

It’s only useful to explicitly copy an array if you’re going to change it in-place. This doesn’t come up often because Awkward Arrays are immutable. That is to say, the Awkward Array library doesn’t have any operations that change an array in-place, but the data in the array might be owned by another library that can change it in-place.

For example, if the array comes from NumPy:

>>> underlying_array = np.array([1.1, 2.2, 3.3, 4.4, 5.5])
>>> wrapper = ak.Array(underlying_array)
>>> duplicate = ak.copy(wrapper)
>>> underlying_array[2] = 123
>>> underlying_array
array([  1.1,   2.2, 123. ,   4.4,   5.5])
>>> wrapper
<Array [1.1, 2.2, 123, 4.4, 5.5] type='5 * float64'>
>>> duplicate
<Array [1.1, 2.2, 3.3, 4.4, 5.5] type='5 * float64'>

There is an exception to this rule: you can add fields to records in an ak.Array in-place. However, this changes the ak.Array wrapper without affecting the underlying layout data (it replaces its layout), so a shallow copy will do:

>>> original = ak.Array([{"x": 1}, {"x": 2}, {"x": 3}])
>>> shallow_copy = copy.copy(original)
>>> shallow_copy["y"] = original.x**2
>>> shallow_copy
<Array [{x: 1, y: 1}, ... y: 4}, {x: 3, y: 9}] type='3 * {"x": int64, "y": int64}'>
>>> original
<Array [{x: 1}, {x: 2}, {x: 3}] type='3 * {"x": int64}'>

This is key to Awkward Array’s efficiency (memory and speed): operations that only change part of a structure re-use pieces from the original (“structural sharing”). Changing data in-place would result in many surprising long-distance changes, so we don’t support it. However, an ak.Array’s data might come from a mutable third-party library, so this function allows you to make a true copy.