In this article, you will learn how to easily create a **ggplot histogram with density curve in R** using a secondary y-axis. We’ll use the `ggpubr`

package to create the plots and the `cowplot`

package to align the graphs.

Contents:

## Prerequisites

Load the required R packages:

```
library(ggpubr)
library(cowplot)
```

## Data preparation

```
set.seed(1234)
wdata = data.frame(
sex = factor(rep(c("F", "M"), each=200)),
weight = c(rnorm(200, 55), rnorm(200, 58)))
head(wdata)
```

```
## sex weight
## 1 F 53.8
## 2 F 55.3
## 3 F 56.1
## 4 F 52.7
## 5 F 55.4
## 6 F 55.5
```

## Create histogram with density distribution on the same y axis

```
# Basic histogram without the density curve
gghistogram(
wdata, x = "weight",
add = "mean", rug = TRUE,
fill = "sex", palette = c("#00AFBB", "#E7B800")
)
```

```
# Add the density curve on the same axis
gghistogram(
wdata, x = "weight", y = "..density..",
add = "mean", rug = TRUE,
fill = "sex", palette = c("#00AFBB", "#E7B800"),
add_density = TRUE
)
```

## Using a secondary y-axis for the density distribution

```
# 1. Create the histogram plot
phist <- gghistogram(
wdata, x = "weight",
add = "mean", rug = TRUE,
fill = "sex", palette = c("#00AFBB", "#E7B800")
)
# 2. Create the density plot with y-axis on the right
# Remove x axis elements
pdensity <- ggdensity(
wdata, x = "weight",
color= "sex", palette = c("#00AFBB", "#E7B800"),
alpha = 0
) +
scale_y_continuous(expand = expansion(mult = c(0, 0.05)), position = "right") +
theme_half_open(11, rel_small = 1) +
rremove("x.axis")+
rremove("xlab") +
rremove("x.text") +
rremove("x.ticks") +
rremove("legend")
# 3. Align the two plots and then overlay them.
aligned_plots <- align_plots(phist, pdensity, align="hv", axis="tblr")
ggdraw(aligned_plots[[1]]) + draw_plot(aligned_plots[[2]])
```

## Conclusion

This article describes how to create a ggplot histogram with density curve in R using a secondary y-axis

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