[R] Change the colours of some of the labels of the x-axis

[Rui Barradas]

Hello,

You cannot pass a vector of colors to col.axis, you need to plot the 
axis twice, once the normal axis, like in your code, then overplot just 
those last 2 labels.


xlabels <- seq(trunc(as.POSIXct(first_day, format="%Y-%m-%d-%H-%M"), 
"days"), trunc(as.POSIXct(last_day, format="%Y-%m-%d-%H-%M"), "days"), 
by="12 hours")

plot(df_plot$data_POSIX, df_plot$hs1, type="b",
      xlim = c(min(xlabels), max(xlabels)), ylim=c(0, 10), col="blue", 
xaxt="n", axes=F, main="", xlab="", ylab="Snow height")
lines(df_plot$data_POSIX, df_plot$hs2, ylim=c(0, 10), col="red", type="b")
axis.POSIXct(1, at = xlabels, format="h%H-%d-%m-%y", pos=0, las = 2)
axis.POSIXct(1, at = tail(xlabels, 2),
              format="h%H-%d-%m-%y", pos=0, las = 2, col.axis = "red")

axis(side=2, at=seq(0, 15, 5))



Hope this helps,

Rui Barradas

Às 15:09 de 07/05/20, Stefano Sofia escreveu:
> Dear R users,
> in a plot I need to change the colours of some of the labels of the x-axis.
> In the example below reported, I would like to have the labels of the last and second-last date in red.
> I tried to find the solution searching the web, but I could not understand the hints and I was not sure I could adapt them to my example.
> There might be an easy way to do that?
> 
> Thank you for your attention and your help
> Stefano
> 
> first_day <- "2005-01-23-09-00"
> last_day <- "2005-01-27-09-00"
> first_day_POSIX <- as.POSIXct(first_day, format="%Y-%m-%d-%H-%M")
> last_day_POSIX <- as.POSIXct(last_day, format="%Y-%m-%d-%H-%M")
> df_plot <- data.frame(data_POSIX=seq(first_day_POSIX, last_day_POSIX, by="30 mins"))
> df_plot$hs1 <- 5
> df_plot$hs2 <- 7
> 
> plot(df_plot$data_POSIX, df_plot$hs1, type="b", ylim=c(0, 10), col="blue", xaxt="n", axes=F, main="", xlab="", ylab="Snow height")
> lines(df_plot$data_POSIX, df_plot$hs2, ylim=c(0, 10), col="red", type="b")
> axis.POSIXct(1, at=seq(trunc(as.POSIXct(first_day, format="%Y-%m-%d-%H-%M"), "days"), trunc(as.POSIXct(last_day, format="%Y-%m-%d-%H-%M"), "days"), by="12 hours"), format="h%H-%d-%m-%y", pos=0)
> axis(side=2, at=seq(0, 15, 5))
> 
> 
>           (oo)
> --oOO--( )--OOo----------------
> Stefano Sofia PhD
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> Uff: 071 806 7743
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