'Nest (⊆, ⊃), also called Conditional Enclose or Enclose If Simple (commonly abbreviated as eis), is a monadic primitive function that applies Enclose to the given argument, but only if it is simple. Nest first appeared as an extension to SHARP APL[1] using the glyph ⊃, and was added to Dyalog APL 16.0 using the glyph ⊆.
Examples
Nest is useful when a nested array is expected but the user may supply a simple array instead. For example, consider a function which expects one or more English words in uppercase and counts the words that include the letter E.
EWords←{+/'E'∊¨⍵}
If the user gives multiple words in the usual notation, it works correctly:
EWords 'I' 'ATE' 'DINNER' 'AND' 'WENT' 'TO' 'SLEEP' ⍝ ATE, DINNER, WENT, SLEEP
4
But if the user gives only one word, EWords will count E's in each letter instead, giving the wrong answer:
EWords 'SLEEP'
2
In this case, the programmer can apply Nest to the argument so that the array has a consistent structure.
EWords2←{+/'E'∊¨⊆⍵}
EWords2 'I' 'ATE' 'DINNER' 'AND' 'WENT' 'TO' 'SLEEP'
4
EWords2 'SLEEP'
1
External links
Documentation
References
| APL built-ins [edit]
|
| Primitives (Timeline) |
Functions
|
| Scalar
|
| Monadic
|
Conjugate ∙ Negate ∙ Signum ∙ Reciprocal ∙ Magnitude ∙ Exponential ∙ Natural Logarithm ∙ Floor ∙ Ceiling ∙ Factorial ∙ Not ∙ Pi Times ∙ Roll ∙ Type ∙ Imaginary ∙ Square Root ∙ Round
|
| Dyadic
|
Add ∙ Subtract ∙ Times ∙ Divide ∙ Residue ∙ Power ∙ Logarithm ∙ Minimum ∙ Maximum ∙ Binomial ∙ Comparison functions ∙ Boolean functions (And, Or, Nand, Nor) ∙ GCD ∙ LCM ∙ Circular ∙ Complex ∙ Root
|
| Non-Scalar
|
| Structural
|
Shape ∙ Reshape ∙ Tally ∙ Depth ∙ Ravel ∙ Enlist ∙ Table ∙ Catenate ∙ Reverse ∙ Rotate ∙ Transpose ∙ Raze ∙ Mix ∙ Split ∙ Enclose ∙ Nest ∙ Cut (K) ∙ Pair ∙ Link ∙ Partitioned Enclose ∙ Partition
|
| Selection
|
First ∙ Pick ∙ Take ∙ Drop ∙ Unique ∙ Identity ∙ Stop ∙ Select ∙ Replicate ∙ Expand ∙ Set functions (Intersection ∙ Union ∙ Without) ∙ Bracket indexing ∙ Index ∙ Cartesian Product ∙ Sort
|
| Selector
|
Index generator ∙ Grade ∙ Index Of ∙ Interval Index ∙ Indices ∙ Deal ∙ Prefix and suffix vectors
|
| Computational
|
Match ∙ Not Match ∙ Membership ∙ Find ∙ Nub Sieve ∙ Encode ∙ Decode ∙ Matrix Inverse ∙ Matrix Divide ∙ Format ∙ Execute ∙ Materialise ∙ Range
|
| Operators |
Monadic
|
Each ∙ Commute ∙ Constant ∙ Replicate ∙ Expand ∙ Reduce ∙ Windowed Reduce ∙ Scan ∙ Outer Product ∙ Key ∙ I-Beam ∙ Spawn ∙ Function axis ∙ Identity (Null, Ident)
|
| Dyadic
|
Bind ∙ Compositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner Product ∙ Determinant ∙ Power ∙ At ∙ Under ∙ Rank ∙ Depth ∙ Variant ∙ Stencil ∙ Cut ∙ Direct definition (operator) ∙ Identity (Lev, Dex)
|
| Quad names
|
Index origin ∙ Comparison tolerance ∙ Migration level ∙ Atomic vector
|