Defined in awkward.operations.structure on line 2620.

ak.firsts(array, axis=1, highlevel=True, behavior=None)
  • array – Data from which to select the first elements from nested lists.

  • axis (int) – The dimension at which this operation is applied. The outermost dimension is 0, followed by 1, etc., and negative values count backward from the innermost: -1 is the innermost dimension, -2 is the next level up, etc.

  • highlevel (bool) – If True, return an ak.Array; otherwise, return a low-level ak.layout.Content subclass.

  • behavior (None or dict) – Custom ak.behavior for the output array, if high-level.

Selects the first element of each non-empty list and inserts None for each empty list.

For example,

>>> array = ak.Array([[1.1], [2.2], [], [3.3], [], [], [4.4], [5.5]])
>>> print(ak.firsts(array))
[1.1, 2.2, None, 3.3, None, None, 4.4, 5.5]

See ak.singletons to invert this function.