Tables: Join on numeric keys

Is there a way to do a join on tables using numeric variables as keys? I get the following error message:

Left and right key variables 'Key' and 'Key' include cells containing non-string values.

I know that I could maybe use something like num2str, but that does not seem very efficient, as I have to do it on large tables and inside loops (i.e. many times)...

[Kirby Fears]

This error often happens when you have a cell array containing some strings and some numbers.

If the Key variable is entirely numeric, try converting it to a double array using cell2num. If that fails, then you probably have strings and numeric data mixed together in your Key variable.

A double array or a cell array of strings should work as a Key variable. I'm not sure if a cell array of doubles works or not.