What ⍳ means
Alone it generates indices; between arrays, it performs “index of.” In ⍳5, it gives five indices, starting at the session’s chosen number. A⍳B returns each B value’s first position in A; a missing value gets the position after A.
Kenneth Iverson began developing APL’s notation for mathematical procedures in 1957. His 1962 book A Programming Language presented it; 1960s experiments led to APL/360 in 1968.
Don't confuse it with
1
Combination ideas
2Five indices from the chosen origin.
Misses return A’s next position.
Questions people ask
1Why does ⍳ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
More like this
11
How to type or find ⍳
- Search it as
- APL iota · index generator · index of · APL keyboard
- Shows up in
- Anything that takes text · its shape is whatever your font draws
Windows (Word)
Windows
HTML
⍳CSS
\2373APL keyboard
On an APL keyboard, use the iota key; one online APL course accepts PREFIXi or iiTab.
Codes and encoding1 code points
HTML decimal
⍳
HTML hex
⍳
CSS content
content: "\2373";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%8D%B3
1
On screen
1
Code points
1
JS .length
3
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.