cuminv

cuminv, function

def process cuminv(a: number): zedfunc

Returns a zedfunc that maps cumulative sums of a back to positions along the specified sort order.

• a: non-negative values to accumulate.

Examples

table Buckets = with
  [| as Step, as Qty |]
  [| 1, 2 |]
  [| 2, 1 |]
  [| 3, 3 |]

z = cuminv(Buckets.Qty) sort Buckets.Step

table X = with
  [| as CumQty |]
  [| 1 |]
  [| 2 |]
  [| 3 |]
  [| 4 |]
  [| 5 |]
  [| 6 |]

X.Step = valueAt(z, X.CumQty)

show table "Inverse" with
  X.CumQty
  X.Step

This produces the following table:

Remarks

cuminv requires a sort order. Use by to compute independent zedfuncs per group.

The returned zedfunc can be queried with valueAt. For a cumulative sum s, valueAt(z, s) returns the first position where the cumulative sum reaches s or more.

Errors

cuminv expects non-negative values. A negative value triggers a fatal error:

‘cuminv()’ expects non-negative values. Found -20 at index 3

See also

• cumsum