Propeller Manual

LOOKDOWN, LOOKDOWNZ – Spin Language Reference
LOOKDOWN, LOOKDOWNZ
Command: Get the index of a value in a list.
((PUB ┆ PRI))
LOOKDOWN ( Value : ExpressionList )
((PUB ┆ PRI))
LOOKDOWNZ ( Value : ExpressionList )
Returns: One-based index position (LOOKDOWN) or a zero-based index position (LOOKDOWNZ) of
Value in ExpressionList, or 0 if Value not found.
•
Value is an expression indicating the value to find in ExpressionList.
•
ExpressionList is a comma-separated list of expressions. Quoted strings of characters
are also allowed; they are treated as a comma-separated list of characters.
Explanation
LOOKDOWN and LOOKDOWNZ are commands that retrieve indexes of values from a list of values.
LOOKDOWN returns the one-based index position (1..N) of Value from ExpressionList.
LOOKDOWNZ is just like LOOKDOWN except it returns the zero-based index position (0..N−1). For
both commands, if Value is not found in ExpressionList then 0 is returned.
Using LOOKDOWN or LOOKDOWNZ
LOOKDOWN and LOOKDOWNZ are useful for mapping a set of non-contiguous numbers (25, -103,
18, etc.) to a set of contiguous numbers (1, 2, 3, etc. –or– 0, 1, 2, etc.) where no algebraic
expression can be found to do so concisely. The following example assumes
Print is a
method created elsewhere.
PUB ShowList | Index
Print(GetIndex(25))
Print(GetIndex(300))
Print(GetIndex(2510))
Print(GetIndex(163))
Print(GetIndex(17))
Print(GetIndex(8000))
Print(GetIndex(3))
PUB GetIndex(Value): Index
Index := lookdown(Value: 25, 300, 2_510, 163, 17, 8_000, 3)
Page 136 · Propeller Manual v1.1