Change background color between day and night in R base

ghz 8months ago ⋅ 140 views

Im trying to change the background color of a graph. My x axis is the day time in format POSIXct and it have measures each 5 minutes. In the Y-axis I have numeric data of clorophyll (chla) measures and I have added also added solar radiation data (PARuw) using PAR(new = TRUE). Those 3 variables are in a data frame named Spring. This is my plot:

par(mfrow=c(1, 1), mar=c(2, 3, 1, 3))

plot(Spring$date_time, Spring$chla, xlab="", ylab="", type="n", 
     ylim=c(0, 6), las=1)
points(Spring$date_time, Spring$chla, pch=21, col="forestgreen", 
       bg="forestgreen", cex=.8)

lines(Spring$date_time, Spring$chla, col="forestgreen", lwd=5)

par(new=TRUE)

plot(Spring$date_time, Spring$PARuw, xlab="", ylab="", xaxt="n", 
     type="n", yaxt="n")

points(Spring$date_time, Spring$PARuw, pch=21, col="yellow2", 
       bg="yellow2", cex=.8)

lines(Spring$date_time, Spring$PARuw, col="yellow2", lwd=5)
axis(side=4, at=seq(0, 1200, by=200), labels=seq(0, 1200, by=200), las=1)

I add head and tail of the data frame:

date_time             PARuw  chla
1 2023-04-23 02:00:00 1.954 4.735
2 2023-04-23 02:05:00 1.971 4.769
3 2023-04-23 02:10:00 1.736 4.671
4 2023-04-23 02:15:00 1.586 4.616
5 2023-04-23 02:20:00 1.566 4.912
6 2023-04-23 02:25:00 1.686 4.615 

date_time              PARuw  chla
283 2023-04-24 01:30:00 2.439 5.511
284 2023-04-24 01:35:00 2.250 5.402
285 2023-04-24 01:40:00 2.443 5.381
286 2023-04-24 01:45:00 2.330 5.386
287 2023-04-24 01:50:00 2.220 5.310
288 2023-04-24 01:55:00 2.472 5.313

enter image description here

I have tryed to differentiate day and night using PARuw > 20 (if this is true then day) and use this on polygon(function) but I dont know how to do it well.

Answers

To differentiate between day and night in your plot and change the background color accordingly, you can indeed use the polygon() function to create a shaded area on the plot. Here's how you can do it:

# Set up plot
par(mfrow=c(1, 1), mar=c(2, 3, 1, 3))
plot(Spring$date_time, Spring$chla, xlab="", ylab="", type="n", 
     ylim=c(0, 6), las=1)
points(Spring$date_time, Spring$chla, pch=21, col="forestgreen", 
       bg="forestgreen", cex=.8)
lines(Spring$date_time, Spring$chla, col="forestgreen", lwd=5)

# Add shaded area for day and night
day_indices <- Spring$PARuw > 20
night_indices <- !day_indices

polygon(c(Spring$date_time[which(day_indices)], rev(Spring$date_time[which(day_indices)])), 
        c(rep(0, sum(day_indices)), rev(rep(6, sum(day_indices)))), 
        col="lightblue", border=NA)

polygon(c(Spring$date_time[which(night_indices)], rev(Spring$date_time[which(night_indices)])), 
        c(rep(0, sum(night_indices)), rev(rep(6, sum(night_indices)))), 
        col="darkblue", border=NA)

# Add solar radiation on secondary y-axis
par(new=TRUE)
plot(Spring$date_time, Spring$PARuw, xlab="", ylab="", xaxt="n", 
     type="n", yaxt="n")
points(Spring$date_time, Spring$PARuw, pch=21, col="yellow2", 
       bg="yellow2", cex=.8)
lines(Spring$date_time, Spring$PARuw, col="yellow2", lwd=5)
axis(side=4, at=seq(0, 1200, by=200), labels=seq(0, 1200, by=200), las=1)

This code will shade the area between day and night on the plot using light blue for day and dark blue for night based on the threshold of PARuw > 20. Adjust the shading and threshold values as needed.

#r