SciDB update function (AFL)?


I use SciDB 14.12.
I’m looking for the update function.

array A: original data
array B: Update the value when z=1 to A (Wish…)
(A and B same schema - attribute: val1, val2 / dimension: x, y, z)

The dimension of B may be only ‘z’.
I tried to use store, merge, insert, etc, but overwriting the entire value.

Is there any way to do this in the AFL ?
Please give me instructions