[R] variable name to hist within apply?

Thomas Lumley thomas at biostat.washington.edu
Fri Mar 10 20:35:33 CET 2000

On 10 Mar 2000, Brian P. Flaherty wrote:

> Hello,
> After spending sometime trying to generate histograms of all the
> numeric variables in a data frame using a for loop, I realized I could
> use apply to create the histograms.  This was one of those few moments
> when I `see' the alternative to looping.
> So, I can generate all the histograms with this command:
>apply(toblo.df[,-c(40,52)],2,hist) # 40 and 52 are ID's 
> When I do this, the name of each histogram is "Histogram of
> newX[,i]".  Just out of curiosity, where does `newX[,i]' come from?
> The help page for hist, it says the data argument is `x'.

Yes, but the argument with which hist is called is newX[,i] (if you look
inside the code for apply)
> The problem with this naming style is that there are over 100
> variables in this data set and it would be nice if the name of each
> variable was above the histogram, instead of an `i'.  How do I get the
> variable name into the title of the histogram?  I have tried a lot of
> things including:

	function (i) hist(toblo.df[,i],main=names(toblo.df)[i]))

should work.  We don't have an analogue of the lisp mapcar function which
takes multiple data arguments (like the data and the names in this case).


Thomas Lumley
Assistant Professor, Biostatistics
University of Washington, Seattle

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