Label individual panels in a multi-panel ggplot2

Question

I'm interested in trying to create simple corner labels for a multipanel figure I am preparing in ggplot. This is similar to this previously asked question, but the answers only explained how to include a label at the top of the plot, not produce a corner label in the format required by many journals. I hope to replicate something similar to the `plotrix` function `corner.label()` in `ggplot2`. Here is an example using `plottrix` of what I would like to recreate in `ggplot2`. ``` require(plotrix) foo1<-rnorm(50,25,5) foo2<-rpois(50,25) foo3<-rbinom(50,25,0.5) foo4<-rnbinom(50,25,0.5) par(mfrow=c(2,2)) hist(foo1) corner.label(label='a',figcorner=T) hist(foo2) corner.label(label='b',figcorner=T) hist(foo3) corner.label(label='c',figcorner=T) hist(foo4) corner.label(label='d',figcorner=T) ``` This produces the following: Thanks for any help in advance!

Accepted Answer

I had the same problem and came up with the following solution, which is a bit different:

loading r packages

```
library(ggplot2)
library(grid)
library(gridExtra)
```

example data

```
a <- 1:20
b <- sample(a, 20)
c <- sample(b, 20)
d <- sample(c, 20)
```

create a data frame

```
mydata   <- data.frame(a, b, c, d)
```

create example plots

```
myplot1  <- ggplot(mydata, aes(x=a, y=b)) + geom_point()
myplot2  <- ggplot(mydata, aes(x=b, y=c)) + geom_point()
myplot3  <- ggplot(mydata, aes(x=c, y=d)) + geom_point()
myplot4  <- ggplot(mydata, aes(x=d, y=a)) + geom_point()
```

set corner labels

```
myplot1 <- arrangeGrob(myplot1, top = textGrob("A", x = unit(0, "npc")
         , y   = unit(1, "npc"), just=c("left","top"),
         gp=gpar(col="black", fontsize=18, fontfamily="Times Roman")))

myplot2 <- arrangeGrob(myplot2, top = textGrob("B", x = unit(0, "npc")
         , y = unit(1, "npc"), just=c("left","top"),
         gp=gpar(col="black", fontsize=18, fontfamily="Times Roman")))

myplot3 <- arrangeGrob(myplot3, top = textGrob("C", x = unit(0, "npc")
        , y  = unit(1, "npc"), just=c("left","top"),
        gp=gpar(col="black", fontsize=18, fontfamily="Times Roman")))

myplot4 <- arrangeGrob(myplot4, top = textGrob("D", x = unit(0, "npc")
        , y = unit(1, "npc"), just=c("left","top"),
        gp=gpar(col="black",    fontsize=18, fontfamily="Times Roman")))
```

plotting all plots on one page

```
grid.arrange(myplot1, myplot2, myplot3, myplot4, ncol = 2)
```

Label individual panels in a multi-panel ggplot2

Solution

Problem

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