Use the Loc() function or the Contains() function to find values in a list:
Loc( list, value );
Contains( list, value );
Loc() and Contains() return the positions of the values. Loc() returns the results in a matrix, and Contains() returns the results as a number.
Notes: 
The Loc function returns each occurrence of a repeated value. Contains() returns only the first occurrence of a repeated value.
If the value is not found, the Loc function returns an empty matrix and Contains() returns a zero.
To assess whether an item is in a list, use Loc() and Contains() with >0. A returned value of zero means that the item is not in the list. A returned value of 1 means that the item is in the list at least once.
nameList = {"Katie", "Louise", "Jane", "Jane"};
numList = {2, 4, 6, 8, 8};
Search for the value "Katie" in the nameList:
Loc( nameList, "Katie" );
[1]
Contains( nameList, "Katie" );
1
Search for the value "Erin" in the nameList:
Loc( nameList, "Erin" );
[]
Contains( nameList, "Erin" );
0
Search for the number 8 in the numList:
Loc( numList, 8 );
[4, 5]
Contains( numList, 8 );
4
Find out if the number 5 exists in the numList:
NRow( Loc( numList, 5 ) ) > 0;
0
Contains( numList, 5 ) > 0;
0

Help created on 10/11/2018