[R] readMat - how to retrieve the variables

[Eduardo M. A. M.Mendes]

Hello

I have a matlab MAT file that contains one single variable: a.  The
structure of a is as follows:

a.river1.flow (flow values)
a.river1.date_flow (date)
a.river1.precip (precipitation values)
a.river1.date_precip
a.river2.flow
a.river2.date_flow
a.river2.precip
a.river2.date_precip

I have used readMat to load the variable a in R, however I have no idea how
readMat translates a.  I managed to get some values out of
data=readMat("matfile.mat")

data$a[,,1]$river1[,,1]$flow  -> Why do I need [,,1]?  Why not
data$a$river1$flow?

Many thanks

Ed