CharacterCounts

CharacterCounts["string"] gives an association whose keys are the distinct characters in string, and whose values give the number of times those characters appear.

CharacterCounts["string", n] gives counts of distinct n-grams consisting of runs of n characters.

Examples

Count characters in a string:

CharacterCounts["hello"]
(* <|"h" -> 1, "e" -> 1, "l" -> 2, "o" -> 1|> *)

Count bigrams:

CharacterCounts["banana", 2]
(* <|"ba" -> 1, "an" -> 2, "na" -> 2|> *)

Please visit the official Wolfram Language Reference for more details.