ParLongData object can hold values that are easy
to specify (like col="clusters" or pch="symbol") but that can not
be directly used by graphical functions plotTrajMeans and
plotTrajMeans3d. This function modify theses values to
make them fit with plotTrajMeans and plotTrajMeans3d expectations.
The field col and pch are the ones concern by this
function.
If y is a Partition, col and pch are
extanded to fit with the number of individual. If y is a number of
clusters, col and pch are extanded to fit with the
number of clusters.
If col='clusters', a color is affected to each clusters. Then
the field col receive a vector of color such that each
individual (if y is a Partition) or each clusters (if
y is a number of clusters) get its corresponding color.
If pch='letters', a letters is affected to each clusters. Then
the field pch receive a vector of letters such that each
individual (if y is a Partition) or each clusters (if
y is a number of clusters) get its corresponding letters.
Same if pch='symbols'.