Conditionally format data in spreadsheet column, but only when it changes

Question

Say I have this data in a Google Spreadsheet:

cat
cat
mouse
mouse
mouse
cat
dog
dog

And I only want to apply conditional formatting to the ones in brackets [] (so I can hide them but still calculate with them)

cat
[cat]
mouse
[mouse]
[mouse]
cat
dog
[dog]

How do I do it? Merging cells won't work because the data needs to be entered line by line and I don't see the option in conditional formatting or when searching around the web.

Answer 1

Assume that the data is the column A and start on row 2,

1. Select the data
2. Click on menu Format > Conditional formatting
3. On the Conditional formatting rules side panel, go to Format cell if and select "Custom formula"
4. Add the following formula

=A2=A1

5. Click on the Done button.