# [R] how to use by() and hist()

Mark Myatt mark at myatt.demon.co.uk
Tue May 8 11:12:09 CEST 2001

```David White <dwhite at ling.ohio-state.edu> writes:

>I'm using R 1.2.2 on Sun Solaris.
>
>I have  data frame with 4 levels of factor "type". See the example data
>frame below.
>     type            token     variance
>20   ku n031ku10.10msmeanc  77199422
>21   ku n031ku11.10msmeanc  55682249
>22   ku n031ku12.10msmeanc  52003965
>23   ti n031ti01.10msmeanc  54511040
>24   ti n031ti02.10msmeanc  58940197
>25   ti n031ti03.10msmeanc  46918442
>
>I'd like to plot histograms by token type as listed in column 1 above.
>I tried
>by(allvariances[,3], allvariances[,1], hist)
>this worked well, but provided histograms with different numbers of bins
>for each token type.
>
>I also tried
> by(allvariances[,3], allvariances[,1], hist(breaks=4))
>to specify the number of bins. Hist then complained that I had not
>specified a value for the data to be plotted.

The syntax for by() is

by(data, INDICES, FUN, ...)

with:

...     further arguments to FUN.

Try:

by(allvariances[,3], allvariances[,1], hist, breaks=4)

The arguments to hist() are specified in the ... list.

>A related question: I'd like to see subsets of the data based on the
>levels of factor "type". So in the example above, I'd like see, say, all
>observations of type "tu". Any pointers on how to do that?

To see all subsets use by:

by(allvariances, type, print)

as this uses the default print() method for the data.frame.

To see a single subset use, surprise, subset():

subset(allvariances, type == "tu"]

I hope that helps.

Mark

--
Mark Myatt

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```