This works fine
data = c(1,3,2)
max_y <- max(data)
plot_colors <- c("blue")
plot(data, type="l", col=plot_colors[1], ylim=c(0,max_y), axes=FALSE, xlab=expression(e[3]))
axis(1, at=c(1,2,3), lab=expression(e[1],e[2],e[3]) )
But I would like to read the labels on the x-axis from a file. I tried the following:
data = c(1,3,2)
names = vector("expression",3)
names[1] = "e[1]"
names[2] = "e[2]"
names[3] = "e[3]"
max_y <- max(data)
plot_colors <- c("blue")
plot(data, type="l", col=plot_colors[1], ylim=c(0,max_y), axes=FALSE, xlab=expression(e[3]))
axis(1, at=c(1,2,3), lab=names )
I tried substitute:
axis(1, at=c(1,2,3), lab=substitute(expression(a), list(a="e[1],e[2],e[3]")) )
but this also did not work. Any suggestion?
What you want is ?parse:
names = c('e[1]', 'e[2]', 'e[3]')
namesExp = do.call(c, lapply(names, function(x) parse(text = x)))
plot(c(1,3,2), type='l', col='blue', axes=FALSE, xlab = expression(e[3]))
axis(3, at=c(1,2,3), lab = names)
axis(1, at=c(1,2,3), lab = namesExp)
Above, lapply returns a list of expressions:
> print(lapply(names, function(x) parse(text = x)))
[[1]]
expression(e[1])
[[2]]
expression(e[2])
[[3]]
expression(e[3])
The do.call just non-recusrively unlists it (also can use unlist(lapply(names, function(x) parse(text = x)), recursive = F)):
> print(do.call(c, lapply(names, function(x) parse(text = x))))
expression(e[1], e[2], e[3])