whichever

whichever(T.A : ‘a) 🡒 ‘a, aggregator

The aggregator returns one value for each group if the group is not empty.

Example:

table T = with
  [| as A, as B |]
  [| "hello", "a" |]
  [| "hello", "a" |]
  [| "hello", "b" |]
  [| "world", "b" |]
  [| "world", "c" |]

table G[gdim] = by T.B

where T.B != "c"
  show table "" a1b4 with
    gdim
    whichever(T.A)
    group by gdim

When the group is empty, the default value for the data type is used.

The result of the whichever aggregator is deterministic - i.e. running the script twice over the same data yields the same result - but the ordering of the data cannot be relied upon. This aggregator is intended as a faster alternative to the use of first or last without introducing an ordering when it is not needed.

See also

whichever, contextual keyword

The contextual keyword whichever can be used as a modifier for the table creation through the keyword by. Using the whichever modifier allows values from the original table to be broadcast into the newly created table. When the modifier whichever is present, the table creation discards all lines for every group except 1 line arbitrarily chosen.

table T = with
  [| as Code, as X |]
  [| "FR",    1    |]
  [| "US",    2    |]
  [| "UK",    3    |]
  [| "FR",    4    |]

table Countries[c] = whichever by T.Code
Countries.X = T.X // broadcast allowed due to 'whichever' modifier
show table "Countries" a1b3 with c, Countries.X // the line 'X == 4' is dropped

In the above script, removing the whichever modifier prevents the script from compiling as the broadcast Countries.X = T.X is rejected.

In practice, it is frequently expected that the whichever by construct would happen in a situation where the choice of the duplicate has no effect because all lines are identical across all the vectors (unlike the example above).