Delete¶

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description¶

Delete[expr, n]

deletes the element at position n in expr.

Examples (6)¶

Every input below was run against the current Mathilda build and its output recorded.

Basic examples (2)¶

In[1]:= Delete[<|"a" -> 1, "b" -> 2, "c" -> 3|>, {Key["b"]}]
Out[1]= <|"a" -> 1, "c" -> 3|>

In[2]:= Delete[<|"a" -> <|"x" -> 5, "y" -> 6|>|>, {Key["a"], Key["x"]}]
Out[2]= <|"a" -> <|"y" -> 6|>|>

Applications (4)¶

In[3]:= Delete[{a, b, c, d}, 2]
Out[3]= {a, c, d}

Negative indices count from the end

In[4]:= Delete[{a, b, c, d}, -1]
Out[4]= {a, b, c}

A list of positions deletes several at once

In[5]:= Delete[{a, b, c, d}, {{1}, {3}}]
Out[5]= {b, d}

Works on any head

In[6]:= Delete[f[a, b, c], 2]
Out[6]= f[a, c]

Implementation notes¶

builtin_delete (in src/part.c) drives the recursive helper delete_path, which walks an integer position (or position path) into the expression tree and removes the targeted element by rebuilding the enclosing function with all arguments except that index. Negative indices count from the end, position 0 targets the head (replaced by a Sequence[...] of the remaining parts), and out-of-range indices leave the structure unchanged.

Attributes: none registered.

References¶

See also: KeyDrop

Source: src/part.c
Specification: docs/spec/builtins/data-structures.md
Tests: tests/test_assoc_forms.c
Tests: tests/test_association.c
Tests: tests/test_packed_list.c
Tests: tests/test_part.c

Notes & additional examples¶

Notes¶

Delete[expr, n] removes the element at position n, rebuilding the enclosing expression without it; negative indices count from the end, and a position path {i, j, ...} reaches a nested element. A list of positions {{p1}, {p2}, ...} deletes each of them in one call. Delete works on any head, not just List. Unlike Drop, which removes a count or a strided range, Delete targets positions explicitly; out-of-range positions leave the structure unchanged.