ggplot legend list is larger than page

Question

I have a plot in R which has a very large number of sample groups, and therefore the legend is larger than the page size and is cut off. I understand that this is not publication quality, but I need to know the colours to be able to make the legend in Illustrator.

Is there a way to make the page size much bigger or somehow change the legend format so that I can include all the keys? The reason for this is so that I can open the PDF in Illustrator and get the colours for each sample to create a new legend that will be for publication. I thought that maybe there is a clipping mask, and that the actual legend will be preserved, but when I opened in Illustrator, the legend was actually cut at the page ends1.

As was suggested in the comments below I gave nrow a try which helped break the legends up but now the entire page is just legends.

ggplot(purine.n, aes(x=variable, y=value, colour=metabolite_gene, shape=variable))
+geom_abline(slope=0)
+geom_point(size=4, position=position_dodge(width=0.08))
+scale_y_continuous(limit=c(-3.5,5.5), breaks=c(-3,-2,-1,0,1,2,3,4,5))
+scale_shape_manual(values=c(16,17,17), guide=F)
+theme_bw()
+theme(legend.key=element_blank(), legend.key.size=unit(1,"point"))
+guides(colour=guide_legend(nrow=16))

Answer 1

As was suggested in the comments, nrow was the answer to my problem. I had to adjust the value to get the right number of rows to fit my legend. Below is the completed code that worked. There's more tweaking I need to do, like change page size to help make things look better, but that is out of the scope of this question.

ggplot(data.n, aes(x=variable, y=value, colour=metabolite_gene, shape=variable))
+geom_abline(slope=0)+geom_point(size=4, position=position_dodge(width=0.08))
+scale_y_continuous(limit=c(-3.5,5.5), breaks=c(-3,-2,-1,0,1,2,3,4,5))
+scale_shape_manual(values=c(16,17,17), guide=F)
+theme_bw()
+theme(legend.key=element_blank(), legend.key.size=unit(1,"point"))
+guides(colour=guide_legend(nrow=30))