Today I spend quite some time trying to figure out why I couldn’t use the `scatterplot`

function (from the package `car`

) for one specific variable, while it worked for every other variable. I got stuck at the error “Error in if (transform != FALSE | length(transform) == ncol(x)) { : argument is of length zero.”

It was only when I used `str`

on the variables to examine the structure that I realized that the scatterplot function does not work with scales. So, normally I could use `scatterplot(y~x | country)`

. In this particular case, I used `x <- scale(x1) + scale(x2) +... `

to create the new variable. `scatterplot(y~x1 | country)`

worked perfectly, as did `scatterplot(y~x2 | country)`

, but the scale did not. It turns out the scale function also adds additional information, which breaks the scatterplot function. Once I knew this, the solution seemed obvious: filter out this additional information by using `as.numeric`

: `scatterplot(y~as.numeric(x) | country)`

.