Counting number of occurrences in column?

Question

What would be a good approach to calculate the number of occurrences in a spreadsheet column? Can this be done with a single array formula?

Example (column A is input, columns B and C are to be auto-generated):

|   A   |   B   |   C   |
+-------+-------+-------+
| Name  | Name  | Count |
+-------+-------+-------+
| Joe   | Joe   |     2 |
| Lisa  | Lisa  |     3 |
| Jenny | Jenny |     2 |
| Lisa  |       |       |
| Lisa  |       |       |
| Joe   |       |       |
| Jenny |       |       |

Answer 1

Try:

=ArrayFormula(QUERY(A:A&{"",""};"select Col1, count(Col2) where Col1 != '' group by Col1 label count(Col2) 'Count'";1))

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22/07/2014 Some time in the last month, Sheets has started supporting more flexible concatenation of arrays, using an embedded array. So the solution may be shortened slightly to:

=QUERY({A:A,A:A},"select Col1, count(Col2) where Col1 != '' group by Col1 label count(Col2) 'Count'",1)