Last

The last element of a collection.

✓ checked against that system · ! checked, with disagreements (hover a chip)Wolfram LanguageLast!↗

Last(collection)the last element of the collection.

Last(collection, default)default when the collection is empty, instead of the last element.

Last(expr)the last operand of any expression, not just a collection.

Typed signatures

Type	Package	Applies
(xs: indexed_collection<any>) -> any	compute-engine	always
(any, any?) -> any	combinatoricsreplaces compute-engine	always

Domain: Collections

Details

• $Last(c) = At(c, -1)$. See At.
• Positional indexing from the front (index 1) and back (negative indices).
• Complements First for the other end of a collection.
• A second argument supplies a default for an empty collection, instead of $Missing$.
• Works on the operands of any expression, not just a collection's elements.

Examples

3 more kept as data, checked against the oracles

Basic #

live ↗

In$\mathrm{Last}(\bigl\lbrack1, 2, 3\bigr\rbrack)$Out$3$

live ↗

In$\mathrm{Last}(\bigl\lbrack10, 20, 30\bigr\rbrack)$Out$30$

live ↗

In$\mathrm{Last}(\bigl\lbrack a, b, c\bigr\rbrack)$Out$c$

An empty list yields the supplied default

live ↗

In$\mathrm{Last}(\bigl\lbrack\bigr\rbrack, x)$Out$x$

live ↗

In$\mathrm{Last}(\bigl\lbrack\bigl\lbrack a, b\bigr\rbrack, \bigl\lbrack c, d\bigr\rbrack, \bigl\lbrack k, f\bigr\rbrack\bigr\rbrack)$Out$\bigl\lbrack k, f\bigr\rbrack$

Scope #

A second argument supplies a default for an empty collection

live ↗

In$\mathrm{Last}(\bigl\lbrack\bigr\rbrack, 99)$Out$99$

Of a matrix, the last row

live ↗

In$\mathrm{Last}(\bigl\lbrack\bigl\lbrack a, b\bigr\rbrack, \bigl\lbrack c, d\bigr\rbrack, \bigl\lbrack f, g\bigr\rbrack\bigr\rbrack)$Out$\bigl\lbrack f, g\bigr\rbrack$

A lazy Range works too

live ↗

In$\mathrm{Last}(5..10)$Out$10$

Any expression, not just a list: the last term of a sum

live ↗

In$\mathrm{Last}(a^2+b^2)$Out$b^2$

A default is ignored when the collection has a last element

live ↗

In$\mathrm{Last}(\bigl\lbrack a, b\bigr\rbrack, x)$Out$b$

live ↗

In$\mathrm{Last}(\mathrm{SparseArray}(1..100))$Out$100$

Properties #

$Last(c) = At(c, -1)$. See At

live ↗

In$\mathrm{Last}(\bigl\lbrack1, 2, 3\bigr\rbrack)=\bigl\lbrack1, 2, 3\bigr\rbrack[-1]$Out$\mathrm{True}$

Possible issues #

An empty collection has no last element; compute-engine returns the symbol $Missing$

live ↗

In$\mathrm{Last}(\bigl\lbrack\bigr\rbrack)$Out$\mathrm{Missing}$

live ↗

In$\mathrm{Last}(\frac{1}{b})$Out$b$

About

Examples	17
Checked against	Wolfram Language 15 agree1 differ1 unevaluatedmathlib4 4 agree1 error
Crosswalk	Wolfram Language

Implementation

mappedmathlib4packages/oracle/src/mappings.ts

The last element of a list; an empty list fails to elaborate (ours is Missing) rather than defaulting, and so does an expression that is not a list.

See also: First, At