Presumably you want to see a list of duplicates from column A and then
get rid of them. The COUNTIF part of the formula will count how many
items are in the range, and when the formula gets copied down it will
become:
=COUNTIF($A$1:A2,A2)>1
then
=COUNTIF($A$1:A3,A3)>1
etc
So, on row 2 it will look to see if the value in A2 is contained
within the range A1:A2, and on row 3 it will compare A3 with the range
A1:A3 etc. Clearly, A2 will appear at least once in the range A1:A2
and A3 will appear at least once in the range A1:A3, but if these
values appear more than once in the range, then the COUNTIF function
will return a number greater than 1.
The formula as written is a kind of shorthand version of an IF
statement, i.e.:
=IF(COUNTIF($A$1:A1,A1)>1,TRUE,FALSE)
It will return a value of TRUE if the COUNTIF function returns a
number greater than 1, and a FALSE value if the function returns 1. It
will return 1 (i.e. a FALSE value from the formula) only for the first
occurrence of a value in column A - all repeat occurrences will be
flagged as TRUE. So, if you then filter the TRUE values and delete
them, you will be left with the unique values.
Hope this helps.
Pete
