Index Finder

Routine Summary

Returns the index number of an element searched for within a list

Inputs

X - Element that it's finding
L₁ - List that's being searched

Outputs

Ans - Index number of element searched.

Variables Used

{$variable}

Calculator Compatibility

TI-83/84/+/SE/CSE

Author

RogueBantha

//Finds first occurence of X in L1
1+sum(not(cumSum(L1=X)))

//Finds last occurence of X in L1
max((L1=X)cumSum(1 or L1))

Given a value in X, this code will search L1 and return the index number of the first (or last) occurrence of X.
For example, in a list L1={1,2,5,4}, the index value of the element 5 is 3. Storing 5 to X and running this code will return 3.

Error Conditions

The first routine returns 1+dim(L₁) if L1 does not contain X, so if L1={1,2,5,4} and one searches for 9, the code will return 5.

The second routine returns 0 if L1 does not contain X, so L1={1,2,5,4} and one searches for 9, the code will return 0.

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