# `⍋` — Grade up / Grade up by

Function. Keys: `Alt-Backslash 7`. Ranks: `∞` monadic, `∞ ∞` dyadic

`⍋Y` gives indices that sort major cells ascending. Stable; uses
[structural ordering](../evaluation.qmd#equality-and-ordering), without
tolerance. NaN sorts after every other number.

``` bpl
⍋30 10 20          ⍝ [1 2 0]ₓ
v←30 10 20 ⋄ [⍋v]⌷v ⍝ 10 20 30
⍋2 1 2 1           ⍝ [1 3 0 2]ₓ
```

`C⍋Y` uses a character collation array `C`.

``` bpl
"cba"⍋"abc"        ⍝ [2 1 0]ₓ
```

See [`⍒`](del-stile.qmd), and [`<`](less-than.qmd) to sort.

## Inverse

`⍋⁻¹P` gives an array whose grade is the permutation `P`. Any other `P`
is a `DOMAIN` error.

``` bpl
⍋⁻¹2 0 1   ⍝ [1 2 0]ₓ
```