Re: [R] converting column to factor *within* a data frame
On Wed, 5 Nov 2003, Pascal A. Niklaus wrote: Hi all, I repeatedly encounter the following problem: After importing a data set into a data frame, I wish to set a column with numeric values to be a factor, but can't figure out how to do this. Also, I do not wish to write as.factor(x) all the time. I can create a new vector with x - factor(x), but the new vector resides outside the attached data frame. Pascal attach(ngrad) is.factor(STNW) [1] FALSE ngrad$STNW-factor(STNW) ## doesn't work is.factor(STNW) [1] FALSE It does work. It changes ngrad, and not the copy you attached. ngrad$STNW-factor(ngrad$STNW) attach(ngrad) is the correct sequence. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UKFax: +44 1865 272595 __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
RE: [R] converting column to factor *within* a data frame
Your problem is with scoping, not the conversion per se:
attach(ngrad)
is.factor(STNW)
[1] FALSE
At this moment, STNW is the same as ngrad$STNW
ngrad$STNW-factor(STNW) ## doesn't work
Yes it does work, try looking at is.factor(ngrad$STNW)
is.factor(STNW)
[1] FALSE
After you assign to ngrad$STNW, it is no longer the same
thing as the attached STNW. You would need to detach
and re-attach ngrad for this to be so. There's no
automatic synchronisation between the attached STNW
and ngrad$STNW; changing one will not change the other.
My advice is: never use attach() if you can help it. It's an
accident waiting to happen. Get used to typing
dataFrame$varname instead of just varname - that way
you will always get what you expect. Or use with() instead
of attach() in almost every case.
HTH
Simon Fear
Senior Statistician
Syne qua non Ltd
Tel: +44 (0) 1379 69
Fax: +44 (0) 1379 65
email: [EMAIL PROTECTED]
web: http://www.synequanon.com
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