ARRAYINDEXOF
Returns the index of a specified item in an array.
Syntax
=ARRAYINDEXOF(array,value)
Example
In this example, cell F19 contains this array, created with the ARRAY function:
#(123,789,TRUE,FALSE,"Test","a","b","c")
This formula returns 6, the index of "a" in the array:
=ARRAYINDEXOF(F19,"a")