Raze

From APL Wiki
Revision as of 21:28, 10 September 2022 by Adám Brudzewsky (talk | contribs) (Text replacement - "</source>" to "</syntaxhighlight>")
Jump to navigation Jump to search
The Right Shoe symbol <source lang=apl inline>⊃</syntaxhighlight> is more commonly used for First or Mix.

Raze (⊃), <source lang=j inline>;</syntaxhighlight> in J, or Join (∾) in BQN, is a monadic function which combines element arrays of a nested vector along the first axis (in accordance with leading axis theory). Thus, the major cells of the Raze of an array are the major cells of its element arrays: unlike Mix, which removes a level of depth while keeping outer and inner axes separate, Raze merges the outer vector's axis with the first axis of each element. Raze is present in A+, J, and BQN.

Examples

Raze can turn a vector of vectors into a single vector. Unlike Mix, it inserts no fill elements. <source lang=apl> 

     ⊃(2 3 4;0 1;5)

2 3 4 0 1 5 </syntaxhighlight>

Works in: A+

When elements of the argument have rank more than 1, Raze combines them along the leading axis, like Catenate First. In A+, the elements must have the same rank and major cell shape or an error results; in J, lower-rank arrays are promoted to a higher rank and arrays are padded with fills to a common major cell shape. <source lang=apl> 

     ⊃(⍳2 2;-⍳4 2)
0  1
2  3
0 ¯1

¯2 ¯3 ¯4 ¯5 ¯6 ¯7 </syntaxhighlight>

Works in: A+

Properties

Raze is similar to the Catenate reduction <source lang=apl inline>↑⍪/</syntaxhighlight>. If <source lang=apl inline>X</syntaxhighlight> is a vector whose elements have equal and positive rank, then <source lang=apl inline>↑⍪/X</syntaxhighlight> is the Raze of <source lang=apl inline>X</syntaxhighlight>. The definition differs if <source lang=apl inline>X</syntaxhighlight> is a singleton vector with scalar elements, because the Raze of <source lang=apl inline>X</syntaxhighlight> will be a vector while the reduction implementation results in a scalar (or, in NARS2000, a DOMAIN ERROR). This is because Raze treats scalar elements of its argument as singleton vectors, a convention which may be viewed as scalar rank extension or as a result of the idea that a scalar's only major cell is itself.

Raze is the inverse of Partition and Partitioned Enclose on vectors: partitioning, then razing, a vector gives that vector back. It is also an inverse to partition functions which partition major cells along the first axis, although few partition functions do this.

High-rank extension

Raze can be extended to an argument array of rank greater than 1, allowing it to merge block matrices or higher-dimensional structures. This extension is part of BQN, but has not been implemented in any APL, and would not be backwards-compatible in J, since J's Raze implicitly ravels its argument.

The axes of a high-rank argument should be paired with those of its element arrays, starting at the first axis (much like prefix agreement). The elements can be merged without adding fills when the length of an element along a particular axis depends only on its position along that axis in the outer array. That is, in <source lang=apl inline>⊃X</syntaxhighlight>, <source lang=apl inline>⍴¨X</syntaxhighlight> must match <source lang=apl inline>⊃∘.,/S</syntaxhighlight>, where S is a vector containing <source lang=apl inline>≢⍴X</syntaxhighlight> vectors followed by any number of scalars. In this case, the shape of <source lang=apl inline>⊃X</syntaxhighlight> is <source lang=apl inline>+/¨S</syntaxhighlight>. The result can be computed by performing a modified 1-dimensional Raze several times. The modified Raze should maintain some number of leading inner element axes. With the Rank operator (<source lang=apl inline>⍤</syntaxhighlight>) we might write <source lang=apl inline>⍪⍤(1-≢⍴X)/X</syntaxhighlight> for a single step in the process, thus reducing along the last axis and catenating along the same axis.

If the element arrays of <source lang=apl inline>X</syntaxhighlight> do not satisfy the shape requirements, they could be padded with fills to force this requirement to hold.

External links

Documentation

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
Retrieved from ‘https://aplwiki.com/index.php?title=Raze&oldid=9291’