Facetting using ggplot in R

Question

Using the example data:

# day 1

carrots <- data.frame(length = rnorm(100000, 6, 2))
cukes <- data.frame(length = rnorm(50000, 7, 2.5))

#Now, combine your two dataframes into one. First make a new column in each.

carrots$veg <- 'carrot'

cukes$veg <- 'cuke'

#and combine into your new data frame vegLengths

vegLengths <- rbind(carrots, cukes)

#now make your lovely plot

ggplot(vegLengths, aes(length, fill = veg)) + geom_histogram(alpha = 0.5), position = 'identity')

# day 2

carrots <- data.frame(length = rnorm(600000, 6, 2))

cukes <- data.frame(length = rnorm(70000, 7, 2.5))

#Now, combine your two dataframes into one.  First make a new column in each.

carrots$veg <- 'carrot'

cukes$veg <- 'cuke'

#and combine into your new data frame vegLengths

vegLengths <- rbind(carrots, cukes)

#now make your lovely plot

ggplot(vegLengths, aes(length, fill = veg)) + geom_histogram(alpha = 0.5), position = 'identity')

I have a similar dataset and decided to use this for easier understanding. I have two such plots. How to use the faceting option and represent day1 and day2 together in a single plot in order to compare them ?

Answer 1

First you have to combine all the data into one dataframe:

carrots1 <- data.frame(length = rnorm(100000, 6, 2))
cukes1 <- data.frame(length = rnorm(50000, 7, 2.5))
carrots1$veg <- 'carrot'
cukes1$veg <- 'cuke'
vegLengths1 <- rbind(carrots1, cukes1)
vegLengths1$day <- '1'

carrots2 <- data.frame(length = rnorm(600000, 6, 2))
cukes2 <- data.frame(length = rnorm(70000, 7, 2.5))
carrots2$veg <- 'carrot'
cukes2$veg <- 'cuke'
vegLengths2 <- rbind(carrots2, cukes2)
vegLengths2$day <- '2'

vegLengths <- rbind(vegLengths1, vegLengths2)

After you can make a plot with:

require(ggplot2)

ggplot(vegLengths, aes(x=length, fill = veg)) + 
  geom_histogram(binwidth=0.5, alpha = 0.5, position = 'identity') +
  facet_wrap(~ day)

The result: