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I'm trying to make the volcanoplot using my DEGs data with ggplot2, I have 2 groups genes of interest in the DEGs, and I want to display these 2 groups of genes with colors and appear on the top layer of the final volcanoplot. The structure of my dataset as follows:

Genes  Log2FoldChange   pvalue  Groups
A      -1.22            0.003   a
B      -2.23            0.001   a
C      2.52             0.004   b
D      3.23             0.008   b
E      3.43             0.005   c
F      -2.45            0.001   c
H      -0.56            0.432   c
...

Group "a" and "b" include about 20 genes, Group "c" include other thousands of genes.

I used the ggplot2 code to make a volcanoplot, but most of the gene plot of Group "a" and "b" (red and blue) were covered by the plots of Group "c" (grey), how can I force all the gene plots of Group "a" and "b" on the top layer of the Group "c" in order to they can be all displayed. 

r03=ggplot(data,aes(log2FoldChange, -log10(pvalue)))

r03+geom_point(aes(color=Groups))
+scale_color_manual(values=c("blue","grey","red"))
+geom_hline(yintercept=1.3, linetype=3)
+geom_vline(xintercept=c(-1,1), linetype=3)
Anthony_x
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  • I think this might be helpful: https://stackoverflow.com/questions/15706281/controlling-order-of-points-in-ggplot2-in-r There are options available including subsetting data (last drawn is on top), using alpha (transparency), sorting/ordering data, etc. – Ben Sep 08 '19 at 02:04
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    @Ben Your suggestion is really helpful, ggplot2 draws the plot in order of the rows, so I ordered the rows and the genes I wanted could be plotted on the top layer. subset() is also useful. Thank you! – Anthony_x Sep 08 '19 at 14:49

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