reject function used with index function

Hello [mention:67d3e8c7ee954087ae38b3a86b2789c3:e9ed411860ed4f2ba0265705b8793d05] 

This is not sufficient information. Please share the more details. Here is something near to what you have asked for, but not accurate as I am not clear of what you are trying to do and what you have tried.

reject(
  isnull(_),
  index(local!activeTasks,"c26",null)
)

hi [mention:67d3e8c7ee954087ae38b3a86b2789c3:e9ed411860ed4f2ba0265705b8793d05]  could you post your data subset output, please? by seeing that we could post some relevant idea/logic for it 

I prefer to avoid "reject()" and the other primitive looping functions where possible (which is almost everywhere), as a!forEach() does a better job, is more flexible, and is easier to understand.  Here we iterate over an array of "local!activeTasks" (pulling out arbitrary property "myProperty" first using the property() rule, which does the same thing as index() but we're using the appropriate one for the job it's doing here).  When any given iteration is blank, the loop returns an empty set.  (We wrap the whole thing in a!flatten() since otherwise if every iteration returns an empty set, it would give you an array of empty sets, which a!flatten() collapses to the desired single empty set).

a!flatten(
  a!forEach(
    property(local!activeTasks, "myProperty", null()),
    if(
      a!isNotNullOrEmpty(fv!item),
      fv!item,
      {}
    )
  )
)