[R] tree growing with rpart

Saket Joshi joshi at engr.orst.edu
Sat Aug 31 00:52:08 CEST 2002

Hi all,

My sincere apologies to all those who could not understand my previous
question and so could not answer it. I am not a statistitian and neither
have I worked on R for long. So please excuse my naive language. I hope I
can explain my question better this time.

I have a data.frame named 'temp'. The following are the series of commands
that followed after I obtained this data.frame

> x <- rpart(temp)

> attributes(x)
 [1] "frame"     "where"     "call"      "terms"     "cptable"   "splits"
 [7] "method"    "parms"     "control"   "functions" "y"         "ordered"

[1] "rpart"

> x$functions
function (yval, dev, wt, ylevel, digits)
    paste("  mean=", formatg(yval, digits), ", MSE=", formatg(dev/wt,
        digits), sep = "")
<environment: 4494214>

function (yval, dev, wt, ylevel, digits, n, use.n)
    if (use.n) {
        paste(formatg(yval, digits), "\nn=", n, sep = "")
    else {
        paste(formatg(yval, digits))
<environment: 4494214>

> gc()
           used  (Mb) gc trigger  (Mb)
Ncells   330122   8.9    1162530  31.1
Vcells 46072722 351.6   64233246 490.1

> x$functions <- NULL

> gc()
           used  (Mb) gc trigger  (Mb)
Ncells   326469   8.8    1162530  31.1
Vcells 34321042 261.9   64233246 490.1

When the "functions" attribute of x was set to NULL, the storage in the
Vcells reduced from 351.6 Mb to 261.9 Mb as can be seen from the 2 gc()
commands executed above.

I imagined that the rpart object 'x', is storing a pointer by the name of
'functions' to a large amount of data in the Vcells. This data was garbage
collected when the pointer 'functions' was NULLed. However I am not sure
that I am right on this count.

My question is: Is there a way in which the options to rpart or otherwise
can be set so as to never create the pointer 'functions' while fitting the
rpart model in the first place instead of having to delete it later in
order to save memory?

Thanks in advance,

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