Reap

Evaluates an expression together with everything Sow recorded during it.

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Reap(expr)

\{value, \{\{sown, ...\}, ...\}\}

expr

's value, and one list per distinct tag Sow used while evaluating it (untagged sows share one group), in first-appearance order.

\{value, \{\}\}

if nothing was sown.

Reap(expr, tag)Like

Reap(expr)

, but the second element is the list of groups whose tag matches

tag

exactly. With a list of tags it holds one such list per tag, so a tag nothing was sown under gives

\{\}

in its place.

Sow(e, \{tag1, tag2\})

sows under each of its tags.

Typed signatures

Type	Package	Applies
`(any, any?) -> any`	`combinatorics`	always

Domain: Collections

Details

Only exact tag equality is matched here, not Wolfram's fuller pattern-matching form of the second argument.
Sequencing several $Sow$ s in one $expr$ : use $[Last, [List, ...]]$ (Wolfram's $a; b; c$ ), not compute-engine's own $Block$ — see Sow's examples and control.ts's module doc for why.

Examples

Basic #

collect everything sown, untagged sows sharing one group

\mathrm{Reap}(\mathrm{Last}(\bigl\lbrack\mathrm{Sow}(1), \mathrm{Sow}(2), 3\bigr\rbrack))

Out

\bigl\lbrack3, \bigl\lbrack\bigl\lbrack1, 2\bigr\rbrack\bigr\rbrack\bigr\rbrack

nothing sown gives an empty group list

\mathrm{Reap}(5)

Out

\bigl\lbrack5, \bigl\lbrack\bigr\rbrack\bigr\rbrack

\mathrm{Reap}(\sum_{k=10}(\mathrm{Sow}(k^2)+1))

Out

\bigl\lbrack395, \bigl\lbrack\bigl\lbrack1, 4, 9, 16, 25, 36, 49, 64, 81, 100\bigr\rbrack\bigr\rbrack\bigr\rbrack

Scope #

Reap(expr, tag) collects only the matching tag's group

\mathrm{Reap}(\mathrm{Last}(\bigl\lbrack\mathrm{Sow}(1, a), \mathrm{Sow}(2, b), \mathrm{Sow}(3, a), 0\bigr\rbrack), a)

Out

\bigl\lbrack0, \bigl\lbrack\bigl\lbrack1, 3\bigr\rbrack\bigr\rbrack\bigr\rbrack

A list of tags gives one list of groups per tag; a tag nothing was sown under gives $\{\}$

\mathrm{Reap}(\mathrm{Last}(\bigl\lbrack\mathrm{Sow}(1, a), \mathrm{Sow}(2, b), 0\bigr\rbrack), \bigl\lbrack a, c\bigr\rbrack)

Out

\bigl\lbrack0, \bigl\lbrack\bigl\lbrack\bigl\lbrack1\bigr\rbrack\bigr\rbrack, \bigl\lbrack\bigr\rbrack\bigr\rbrack\bigr\rbrack

A list of tags sows under each of them

\mathrm{Reap}(\mathrm{Last}(\bigl\lbrack\mathrm{Sow}(1, \bigl\lbrack a, b\bigr\rbrack), 0\bigr\rbrack), b)

Out

\bigl\lbrack0, \bigl\lbrack\bigl\lbrack1\bigr\rbrack\bigr\rbrack\bigr\rbrack

Properties #

With nothing sown, the result is the value and an empty list of sown items

\mathrm{Reap}(x)

Out

\bigl\lbrack x, \bigl\lbrack\bigr\rbrack\bigr\rbrack

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