Counts
Counts[list]
gives an association whose keys are the distinct elements of list, and whose values give the number of times those elements appear in list.
Examples
Wolfram Research (2014), Counts, Wolfram Language function, https://reference.wolfram.com/language/ref/Counts.html.
Text
Wolfram Research (2014), Counts, Wolfram Language function, https://reference.wolfram.com/language/ref/Counts.html.
CMS
Wolfram Language. 2014. "Counts." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Counts.html.
APA
Wolfram Language. (2014). Counts. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Counts.html