I've seen on different post that specfifying the librairy could help, so by entering the following formula, I though I could solved my problem on my own :
Unfortunately, I encounter the following error :
package 'tm' could not be loaded
The 'tm' package is needed, but don't know how to specify it.
( I've already tried to install TM package & librairy, via R console, but it appears that it's not taken into account by Tableau.)