Grouped bar chart on R using ggplot2

问题:

How do I create a grouped bar chart on R using ggplot2 using this data?

Person Cats Dogs

Mr. A   3   1

Mr. B   4   2

So that it shows that shows number of pets owned per person, with this layout Bar chart of pets

I have a text file with this data and have used read.delim to read the file on R.

I have used this code but it does not produce the bar plot I am looking for.

ggplot(data=pets, aes(x=Person, y=Cats, fill=Dogs)) + geom_bar(stat="identity", position=position_dodge())

I am new to R, any help would be appreciated.

Thanks in advance.

回答1:

To prepare data for grouped bar plot, use melt() function of reshape2 package

I. Loading required packages

    library(reshape2)
    library(ggplot2)

II. Creating data frame df

    df <- data.frame(Person = c("Mr.A","Mr.B"), Cats = c(3,4), Dogs = c(1,2))
    df
    #   Person Cats Dogs
    # 1   Mr.A    3    1
    # 2   Mr.B    4    2

III. Melting data using melt function

    data.m <- melt(df, id.vars='Person')
    data.m
    #   Person variable value
    # 1   Mr.A     Cats     3
    # 2   Mr.B     Cats     4
    # 3   Mr.A     Dogs     1
    3 4   Mr.B     Dogs     2

IV. Grouped Bar plot by Person

   ggplot(data.m, aes(Person, value)) + geom_bar(aes(fill = variable), 
   width = 0.4, position = position_dodge(width=0.5), stat="identity") +  
   theme(legend.position="top", legend.title = 
   element_blank(),axis.title.x=element_blank(), 
   axis.title.y=element_blank())

Legend on top, legend title removed, axis titles removed, adjusted bar widths and space between bars.