changed

changed, process

def process changed(a: _typ): boolean

Returns true if the current value a is different from the previous value; always returns true for the first element. This process aggregator must be used with an ordering option (sort or scan).

• a: The input value to compare with the previous element (generic type).

Examples

table T = with 
  [| as Val |]
  [| "a" |] // changed = true
  [| "a" |]
  [| "b" |] // changed = true
  [| "b" |]
  [| "b" |]
  [| "c" |] // changed = true

show table "" a1b6 with
  T.Val
  changed(T.Val) scan auto

This process aggregator is useful for skipping unchanged lines when persisting sequential data, such as historical prices.

Remarks

This aggregator could be manually reimplemented.

def process changed_bis(next: number) default false with
  keep prev = 0
  changed = prev != next
  prev = next
  return argfirst() or changed