Delete a period and a number at the end of a character string

You just need a simple regular expression:

z_new = gsub("\\.[0-9]*$", "", z)

A few comments:

1. The first argument in gsub is the pattern we are looking for. The second argument is what to replace it with (in this case, nothing).
2. The $ character looks for the pattern at the end of the string
3. [0-9]* looks for 1 or more digits. Alternatively, you could use \\d* or [[:digit:]]*.
4. \\. matches the full stop. We need to escape the full stop with two slashes.

Try this

gsub("\\.[[:digit:]]*$", "", z)