[R] boxplot() from list

[Prof Brian Ripley]

On Sun, 12 Sep 2004, Marc Schwartz wrote:

> On Sun, 2004-09-12 at 10:10, Laura Quinn wrote:
> > I have a list containing 48 objects (each with 30 rows and 4 columns, all
> > numeric), and wish to produce 4 boxplot series (with 48 plots in each) ,
> > one for each column of each object.
> > 
> > Basically I want a boxplot from boxplot(mylist[[]][,i])
> > 
> > for i in 1:4. It seems that I can create a boxplot of length 48 from the
> > entire list, but I don't seem able to subscript to return 4 boxplots from
> > the list - I have also tried to create 4 new lists (one for each column of
> > each object) by using variations on the following, but none seems to work:
> > 
> > newlist<-oldlist[,1]
> > newlist<-oldlist[[]][,1]
> > newlist<-oldlist[[]][,$colone]
> > 
> > can anyone please offer some insight??
> > 
> > Thanks in advance,
> 
> 
> For each individual boxplot, you could do something like:
> 
> boxplot(data.frame(sapply(mylist, function(x) x[, 1])))
> 
> adjusting the index (1) for each of the four columns in your list
> matrices. 
> 
> You can then adjust the additional arguments to boxplot() as you
> require.
> 
> See ?sapply for more information on accessing list member elements and
> returning a vector or matrix.

I think that is overly complex, as boxplot accepts a list.  I had tested
(but decided not to send)

mylist <- vector("list", 48)
for(i in 1:48) mylist[[i]] <- matrix(rnorm(30*4), 30) 

for (J in 1:4) boxplot(lapply(mylist, function(x, j) x[, j], j = J))


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
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, UK                Fax:  +44 1865 272595