How to plot enrichment analysis scatter diagram with ggplot2

library(argparser)
library(ggplot2)

# Incoming parameters
argv <- arg_parser('Draw a scatter plot based on the results of the enrichment analysis')
argv <- add_argument(argv, "--enrich", help = "Enrichment result file")
argv <- add_argument(argv, "--ndot", help = "The figure shows the number of pathways", type = 'numeric')
argv <- add_argument(argv, "--title", help = "Graphic title")
argv <- add_argument(argv, "--prefix", help = "Output picture prefix")
argv <- parse_args(argv)
enrich <- argv$enrich
ndot <- argv$ndot
title <- argv$title
prefix <- argv$prefix

enrich <- read.delim(enrich, header = T, sep = '\t')
enrich <- na.omit(enrich)

# Sort by padj and select ndot pathway drawings
enrich <- enrich[order(enrich$padj, decreasing = F), ]
if(nrow(enrich)>ndot){enrich <- enrich[1:ndot, ]}

#Calculate GeneRatio
ratio <- matrix(as.numeric(unlist(strsplit(as.vector(enrich$GeneRatio),"/"))), ncol = 2, byrow = TRUE)
enrich$GeneRatio <- ratio[,1]/ratio[,2]

#Drawing enrichment scatter plot
p <- ggplot(enrich, aes(x = GeneRatio, y = Description, colour = padj, size = Count))
p <- p + geom_point()
p <- p + scale_colour_gradientn(colours = rainbow(4), guide = "colourbar") + expand_limits(color = seq(0,1,by = 0.25))
p <- p + ggtitle(title) + xlab("GeneRatio") +ylab("")
p <- p + theme_bw() + theme(axis.text = element_text(color = "black", size = 10))
p <- p + theme(panel.border = element_rect(colour = "black"))
p <- p + theme(plot.title = element_text(vjust = 1), legend.key = element_blank())
ggsave(paste(prefix, '.dot.png', sep = ''), plot = p, width = 8, height = 6, type = 'cairo-png')