Forum Discussion
Recursive LAMBDA implementation of Excel's REDUCE function.
Not a question -- just sharing some interesting code. Out of curiosity, I decided to develop an implementation of Excel's REDUCE function as a recursive Excel LAMDA function. I was truly amazed how...
HI SergeiBaklan
I added an explicit stack parameter to the recursive scan and that seems to do the trick.
=LAMBDA(initial_value, array, CLAMBDA,
LET(
_00, "Implementation of SCAN in Excel Lambda",
_01, "accumulator must be a scalar or column vector"
vec, TOROW(array),
rec_L, LAMBDA(stack, acc, cindex, rec_LL,
LET(
cvalue, INDEX(vec, 0, cindex),
new_acc, CLAMBDA(acc, cvalue),
new_stack, HSTACK(stack, new_acc),
IF(
cindex = COLUMNS(vec),
new_stack,
rec_LL(new_stack, new_acc, cindex + 1, rec_LL)
)
)
),
tresult, (rec_L(initial_value, initial_value, 1, rec_L)),
MAP(tresult, LAMBDA(v, IF(ISERROR(v), "", v)))
)
)({1}, {2, 3, 4}, LAMBDA(a, b, VSTACK(a, b)))
Probably need to add code to drop the 1st column - but above seems to be moving in the right direction.
| 1 | 1 | 1 | 1 |
| 2 | 2 | 2 | |
| 3 | 3 | ||
| 4 |
Here is a correct version of the above, with the correct stack initialization. I think this is a valid scan function.
=LAMBDA(initial_value, array, CLAMBDA,
LET(
_00, "Implementation of SCAN in Excel Lambda",
vec, TOROW(array),
rec_L, LAMBDA(stack, acc, cindex, rec_LL,
LET(
cvalue, INDEX(vec, 0, cindex),
new_acc, CLAMBDA(acc, cvalue),
new_stack, IF(cindex = 1, new_acc, HSTACK(stack, new_acc)),
IF(cindex = COLUMNS(vec), new_stack, rec_LL(new_stack, new_acc, cindex + 1, rec_LL))
)
),
tresult, (rec_L("", initial_value, 1, rec_L)),
MAP(tresult, LAMBDA(v, IF(ISERROR(v), "", v)))
)
)({1, 2}, {2, 3, 4}, LAMBDA(a, b, VSTACK(a, b)))