DigitCount

DigitCount[n, b, d] gives the number of d digits in the base-b representation of n.

DigitCount[n, b] gives a list of the numbers of 1, 2, ..., b-1, 0 digits in base b.

DigitCount[n] gives counts of 1, 2, ..., 9, 0 digits in base 10.

Examples

Count 1s in binary:

DigitCount[255, 2, 1]
(* 8 *)

Digit frequency in base 10:

DigitCount[123456789]
(* {1, 1, 1, 1, 1, 1, 1, 1, 1, 0} *)

Please visit the official Wolfram Language Reference for more details.