This Excel LAMBDA function computes the finite difference of a vector

excel-lambda-FINITE_DIFF.txt

/*
FINITE_DIFF function

array is a vector (one column or one row)

1) Check if array is a vector. If not, return #VALUE!

2) Multiply array by similarly sized array of {1, -1, ..., -1}.

3) REDUCE SUM over (2)
*/
FINITE_DIFF = LAMBDA(array, 
    IF(
        AND(ROWS(array)>1,COLUMNS(array)>1), #VALUE!,
        REDUCE(,array * EXPAND(1, ROWS(array), COLUMNS(array), -1), SUM)
    )
);