count()

Returns the number of matches.

When used alone count() gives the total matches seen up to the current line in the file.

Matches can be scoped down to a contained existence test or equality. Counting an equality means a function, term, variable, or header compared to another function, term, variable, or header.

When count() is scoped to its contained value, the count is of the values seen. If it is a bool, the count is the number of Trues and the number of Falses. If an int, it is a count of each value seen.

For example, take count( empty( #zipcode ) )

This use of count() counts the number of times it sees True and False. Whereas, count( #zipcode ) Counts the number of times each value of zipcode is seen.

When counting the values it sees, count() stores the value-integer pairs in a variable under a key identifying the count function. The ID of the count function is a hash by default, making it difficult for a human to understand which count the key represents. To name the count use a qualifier count().

A name qualifier is a name that follows the function name separated by a dot. For example: count.red_cars(#0="red").

count() can take the onmatch qualifier. When there is a contained value and onmatch, count only increments if its contained value matches. For example: $[*][count.onmatch( in(#firstname,"Bug|Bird|Ants") ) == 2]

This path counts first names that match the in() function. If the count equals 2 the row will also match. This is a different behavior from that of other match components in that count is using onmatch to look inward, rather than at its siblings. Bear in mind, count() without a contained value only increments when the row matches. In that case, onmatch would add nothing.

Data signatures
count()
count( [eval: $${\color{green}None}$$ ǁ $${\color{green}Any}$$], ... )

Call signatures
count()
count( [eval: Matchable], ... )

Purpose	Value
Main focus	count() produces a calculated value

Context	Qualifier
Match qualifiers	onmatch
Value qualifiers	onmatch
Name qualifier	optionally expected

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