Editing Yorick (programming language) (section)

=== Indexing ===
Yorick is good at manipulating elements in N-dimensional arrays conveniently with its powerful syntax.

Several elements can be accessed all at once:

<syntaxhighlight lang="rout">
> x=[1,2,3,4,5,6];
> x
[1,2,3,4,5,6]
> x(3:6)
[3,4,5,6]
> x(3:6:2)
[3,5]
> x(6:3:-2)
[6,4]
</syntaxhighlight>

;Arbitrary elements

<syntaxhighlight lang="rout">
> x=[[1,2,3],[4,5,6]]
> x
[[1,2,3],[4,5,6]]
> x([2,1],[1,2])
[[2,1],[5,4]]
> list=where(1<x)
> list
[2,3,4,5,6]
> y=x(list)
> y
[2,3,4,5,6]
</syntaxhighlight>

;Pseudo-index

Like "theading" in [[Perl Data Language|PDL]] and "broadcasting" in [[Numpy]], Yorick has a mechanism to do this:

<syntaxhighlight lang="rout">
> x=[1,2,3]
> x
[1,2,3]
> y=[[1,2,3],[4,5,6]]
> y
[[1,2,3],[4,5,6]]
> y(-,)
[[[1],[2],[3]],[[4],[5],[6]]]
> x(-,)
[[1],[2],[3]]
> x(,-)
[[1,2,3]]
> x(,-)/y
[[1,1,1],[0,0,0]]
> y=[[1.,2,3],[4,5,6]]
> x(,-)/y
[[1,1,1],[0.25,0.4,0.5]]
</syntaxhighlight>

;Rubber index

".." is  a rubber-index to represent zero or more dimensions of the array.

<syntaxhighlight lang="rout">
> x=[[1,2,3],[4,5,6]]
> x
[[1,2,3],[4,5,6]]
> x(..,1)
[1,2,3]
> x(1,..)
[1,4]
> x(2,..,2)
5
</syntaxhighlight>

"*" is a kind of rubber-index to reshape a slice(sub-array) of array to a vector.

<syntaxhighlight lang="rout">
> x(*)
[1,2,3,4,5,6]
</syntaxhighlight>

;Tensor multiplication

[[Tensor]] multiplication is done as follows in Yorick:

 P(,+, )*Q(, +)

means <math>\sum_{j=1}^{j=N}{P_{ijkl}Q_{mnj}}</math>

<syntaxhighlight lang="rout">
> x=[[1,2,3],[4,5,6]]
> x
[[1,2,3],[4,5,6]]
> y=[[7,8],[9,10],[11,12]]
> x(,+)*y(+,)
[[39,54,69],[49,68,87],[59,82,105]]
> x(+,)*y(,+)
[[58,139],[64,154]]
</syntaxhighlight>