Compare value in all cells in a column in Google Sheets

Question

I'm trying to use conditional formatting to make all the values in one column that are the same turn red. I used arrayformula, but I can only get it to do that for the first value in the column.

I tried this in the custom formula and applied it to all the cells in the column: =ARRAYFORMULA(IF(F1:F10=F:F,1,0))

Also I'm no expert here, trying to learn as I go.

So if the column has these values (each in their own cell):

A
A
B
D
B
N
G

I would want the A's and B's to turn red.

Answer 1

Please select ColumnF and apply a Custom formula is of:

=countif(F:F,F1)>1  

Select your format.

COUNTIF

For your locale you might need ; rather than ,.