Let’s make a Histogram using ggplot

First step, import the ggplot2 library

library(ggplot2)

Now let’s look at our data. In this example I am using chickwts from R Data

head(chickwts) str(chickwts)

As you can see above, this data contains 2 columns weight ( numeric) and feed(Factor with 6 levels)

## Histogram

In a histogram, we don’t need to worry about assigning a Y axis, the Y axis is the frequency count of our X variable.

Let’s set our data and x axis in ggplot. Let’s also assign it to variable.

pl <- ggplot(data=chickwts, aes(x=weight))

Now we can use the assigned variable in conjunction with our geom()

pl + geom_histogram(binwidth=10)

In our geom, I set a binwidth. This tells us how wide to make our bars. Setting binwidth to 10 makes each bar 10 units wide.

Let’s give it some color

pl + geom_histogram(binwidth=10, fill="blue")

Now, let’s set our colors based on our 2nd column “feed”. Note how a legend is automatically generated.

pl + geom_histogram(binwidth=10, aes(fill=feed))

For the finishing touch, let’s add some black bordering around our boxes.

pl + geom_histogram(binwidth=10, aes(fill=feed), color="black")

## The Code

library(ggplot2) head(chickwts) #-- look at structure str(chickwts) #set data and x axis value pl <- ggplot(data=chickwts, aes(x=weight)) #create histogram, binwidth 10 pl + geom_histogram(binwidth=10) #change bars to blue pl + geom_histogram(binwidth=10, fill="blue") #set color of bars by feed column values pl + geom_histogram(binwidth=10, aes(fill=feed)) #add black border around boxes pl + geom_histogram(binwidth=10, aes(fill=feed), color="black")