OccurrenceCount

OccurrenceCount, or occurrence count, is the number of times a target value or predicate appears within a data collection, such as an array, string, or database column. It is a basic measure of frequency used in data processing, analysis, and text processing. Computing an occurrence count typically involves iterating over the data and incrementing a counter when the value matches the target or when the item satisfies the condition; if counts for all distinct values are needed, a frequency map or histogram can be built in a single pass.

Common programming language patterns include using built-in facilities or simple loops. In Python, the standard library provides a count method on sequences to count occurrences of a value, and the expression sum(1 for x in sequence if x == target) computes the same result for more complex conditions. In JavaScript, a reduction or a filter-and-length approach can yield the count. In SQL, counting is performed with SELECT COUNT(*) FROM table WHERE column = value.

Performance considerations depend on scope. A single-target count over n items is typically O(n) time and O(1) extra space. Building a full frequency map for all values takes O(n) time and O(k) space, where k is the number of distinct values.

Applications include measuring word or character frequency in text, counting events in logs, and identifying the most frequent value or mode. See also frequency, histogram, and mode.