groupBy package:streamly-core

Given an input stream [a,b,c,...] and a comparison function cmp, the parser assigns the element a to the first group, then if a `cmp` b is True b is also assigned to the same group. If a `cmp` c is True then c is also assigned to the same group and so on. When the comparison fails the parser is terminated. Each group is folded using the Fold f and the result of the fold is the result of the parser.

• Stops - when the comparison fails.
• Fails - never.

>>> :{
runGroupsBy eq =
Stream.fold Fold.toList
. Stream.parseMany (Parser.groupBy eq Fold.toList)
. Stream.fromList
:}

>>> runGroupsBy (<) []
[]

>>> runGroupsBy (<) [1]
[Right [1]]

>>> runGroupsBy (<) [3, 5, 4, 1, 2, 0]
[Right [3,5,4],Right [1,2],Right [0]]

Unlike groupBy this combinator performs a rolling comparison of two successive elements in the input stream. Assuming the input stream is [a,b,c,...] and the comparison function is cmp, the parser first assigns the element a to the first group, then if a `cmp` b is True b is also assigned to the same group. If b `cmp` c is True then c is also assigned to the same group and so on. When the comparison fails the parser is terminated. Each group is folded using the Fold f and the result of the fold is the result of the parser.

• Stops - when the comparison fails.
• Fails - never.

>>> :{
runGroupsByRolling eq =
Stream.fold Fold.toList
. Stream.parseMany (Parser.groupByRolling eq Fold.toList)
. Stream.fromList
:}

>>> runGroupsByRolling (<) []
[]

>>> runGroupsByRolling (<) [1]
[Right [1]]

>>> runGroupsByRolling (<) [3, 5, 4, 1, 2, 0]
[Right [3,5],Right [4],Right [1,2],Right [0]]

Pre-release

Like groupByRolling, but if the predicate is True then collects using the first fold as long as the predicate holds True, if the predicate is False collects using the second fold as long as it remains False. Returns Left for the first case and Right for the second case. For example, if we want to detect sorted sequences in a stream, both ascending and descending cases we can use 'groupByRollingEither (<=) Fold.toList Fold.toList'. Pre-release