I am using R to plot line chart, with the following command
data <- read.table("input_data.txt", header=T, sep="\t")
ind=seq(1,nrow(data),by=2)
pdf(file="result.pdf")
plot_colors <- c("black","red","green","blue","purple","red")
plot(data$column_one, type="l", lty=1, col=plot_colors[1], ann=FALSE)
lines(data$column_two, type="l", lty=2, col=plot_colors[2])
lines(data$column_three, type="o", pch=1, lty=0, col=plot_colors[3], cex=1)
lines(data$column_four, type="o", pch=3, lty=0, col=plot_colors[4], cex=1)
lines(data$column_five, type="o", pch=2, lty=0, col=plot_colors[5], cex=1)
lines(data$column_six, type="o", pch=4, lty=1, col=plot_colors[6], cex=1)
box()
dev.off()
The problem is, I have 500 data points, and the symbol markers are all mashed up on the line, tightly compact on the line. I could not see the symbols on the line.
Is there a way to just show the symbol markers at fixed interval, without them cluttering together?