Once you start becoming more of an R expert user, you will likely need to load several add-on packages for some of your analysis. Once you start doing this, it is likely that two packages use the same name for two different functions. And often these functions do completely different things. In fact, you will encounter this in the next practica where you will need the dplyr package, this is because both the dplyr and the R-base stats package define a filter function.

There are five other examples in dplyr. We know this because when we first load dplyr we see the following message:

The following objects are masked from ‘package:stats’:

    filter, lag

The following objects are masked from ‘package:base’:

    intersect, setdiff, setequal, union

So what does R do when we type filter? Does it use the dplyr function or the stats function? From our previous work we know it uses the dplyr one. But what if we want to use the stats version?

These functions live in different namespaces. R will follow a certain order when searching for a function in these namespaces. You can see the order by typing:


The first entry in this list is the global environment which includes all the objects you define.

So what if we want to use the stats filter instead of the dplyr filter but dplyr appears first in the search list? You can force the use of a specific namespace by using double colons (::) like this:


If we want to be absolutely sure that we use the dplyr filter, we can use


Also note that if we want to use a function in a package without loading the entire package, we can use the double colon as well.

For more on this more advanced topic we recommend the R packages book[16].