Tag: r histograms

R: ggplot using facets

On By Ben Larson Ph.D.In R, VizualizationLeave a comment

In this example I am going to teach you to use facets to add another level to your ggplot data visualizations. In this example we will be working with the ChickWeight data set from R Datasets

First, let’s check out the data by running head()

head(ChickWeight)

facet1.jpg

We have 4 columns in our data, weight, Time, Chick, and Diet.

Now, let’s build our ggplot model. Below, we are setting our model to a variable “p1”. We then set ChickWeight as our data set and the weight column to our x axis. Remember, nothing will happen when running the line below.

p1 <- ggplot(data=ChickWeight, aes(x=weight))

Now lets graph our plot as a histogram – we will set our binwidth to 10 – if any of this confusing you, go back and check out my earlier lessons on ggplot and ggplot histograms

p1 + geom_histogram(binwidth = 10)

facet2.jpg

Let’s now add some color. I am going to set our “fill” to be Diet

p1 + geom_histogram(binwidth = 10, aes(fill=Diet))

facet3.jpg

Now, using facets, I am going to take it one step further and separate this into 4 histograms, one for each diet.

 p1 + geom_histogram(binwidth = 10, aes(fill=Diet)) + facet_grid(Diet~.)

facet4.jpg

The Code

#-- Look at data

head(ChickWeight)

#-- build ggplot model
p1 <- ggplot(data=ChickWeight, aes(x=weight))

#--plot ggplot as histogram
p1 + geom_histogram(binwidth = 10)

#-- set fill color to Diet
p1 + geom_histogram(binwidth = 10, aes(fill=Diet))

#-- create four histograms - one for each Diet
p1 + geom_histogram(binwidth = 10, aes(fill=Diet)) + facet_grid(Diet~.)

 

 

 

R: ggplot – Histograms

On By Ben Larson Ph.D.In R, VizualizationLeave a comment

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)

histogram1.jpg

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.

histogram2

Let’s give it some color

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

histogram3.jpg

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))

histogram4.jpg

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

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

histogram5.jpg

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")