SplitBy

Split a list into runs on which a function is constant.

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

SplitBy(list, f)runs on which $f(element)$ stays the same.

Typed signatures

Type	Package	Applies
(indexed_collection<T>, (T) any -> any) -> list<list<T>> where T	combinatorics	always

Domain: Collections

Details

• Split with the adjacency test "same $f$ value" instead of plain equality.

Examples

Basic #

Runs of the same parity

live ↗

In$\mathrm{SplitBy}(\bigl\lbrack1, 3, 5, 2, 4, 7, 9\bigr\rbrack, \operatorname{\_1}↦\operatorname{\_1}\bmod2)$Out$\bigl\lbrack\bigl\lbrack1, 3, 5\bigr\rbrack, \bigl\lbrack2, 4\bigr\rbrack, \bigl\lbrack7, 9\bigr\rbrack\bigr\rbrack$

Runs with the same value of $\lfloor x/4 \rfloor$

live ↗

In$\mathrm{SplitBy}(\bigl\lbrack1, 2, 3, 4, 5, 6, 7, 8, 9, 10\bigr\rbrack, \operatorname{\_1}↦\lfloor\frac{\operatorname{\_1}}{4}\rfloor)$Out$\bigl\lbrack\bigl\lbrack1, 2, 3\bigr\rbrack, \bigl\lbrack4, 5, 6, 7\bigr\rbrack, \bigl\lbrack8, 9, 10\bigr\rbrack\bigr\rbrack$

Groups consecutive values sharing an integer part

live ↗

In$\mathrm{SplitBy}(1..(1+\frac{1}{2})..5, \mathrm{IntegerPart})$Out$\bigl\lbrack\bigl\lbrack1, \frac{3}{2}\bigr\rbrack, \bigl\lbrack2, \frac{5}{2}\bigr\rbrack, \bigl\lbrack3, \frac{7}{2}\bigr\rbrack, \bigl\lbrack4, \frac{9}{2}\bigr\rbrack, \bigl\lbrack5\bigr\rbrack\bigr\rbrack$

Applications #

Splits wherever the sign value changes

live ↗

In$\mathrm{SplitBy}(\bigl\lbrack3, 0, -4, 3, 3, -2, 0, -3, -4, 5\bigr\rbrack, \mathrm{Sign})$Out$\bigl\lbrack\bigl\lbrack3\bigr\rbrack, \bigl\lbrack0\bigr\rbrack, \bigl\lbrack-4\bigr\rbrack, \bigl\lbrack3, 3\bigr\rbrack, \bigl\lbrack-2\bigr\rbrack, \bigl\lbrack0\bigr\rbrack, \bigl\lbrack-3, -4\bigr\rbrack, \bigl\lbrack5\bigr\rbrack\bigr\rbrack$

About

Examples	4
Checked against	Wolfram Language 4 agree
Crosswalk	Wolfram Language

See also: Split, GatherBy