I'm trying to visualise missing data with the R package VIM. I'm using R version 3.4.0 with RStudio
I've used the function aggr() but the colnames of my dataframe seem to be too long. Thus, some labels of the x axis don't appear. I would like to increase the space at the bottom of the x axis.
library(VIM)
aggr(df)
Here is my dataframe df and the plot I obtain

I've tried with par() function but it doesn't change anything.
aggr(df,mar=c(10,5,5,3))
or
par(mar=c(10,5,5,3))
g=aggr(df,plot=FALSE)
plot(g)
I can reduce the font size with cex.axis but then labels are too small.
aggr(df,cex.axis=.7)
Here is the plot with small axis labels:

I've not find a lot of examples using aggr() that's why I ask for your help. Thank you in advance.