Plot multiple columns with geom_bar()

Question

I recently started programming in R and I am trying to plot several columns using ggplot2.

My data frame looks like this:

mydf <- data.frame(Names, Less, Equal, More)
mydf

    Names Less Equal More
1   Sarah    8    25    8
2   Mark    13    13   13
3   Peter   11    26    5

And to give an idea of how I created this data frame, 'Less' looks like this:

[1]  8 13 11

I want to be able to compare for every name if their scores are less, equal, or more. On the x-axis, I actually want to plot "More", "Less", and "Equal", with different bars for each name. On the y-axis I want to print the score (eg 8, 25...). I want to create multiple bars for each name.

I have tried several things, but I have only succeeded in adding a single value on the y-axis:

test <- ggplot(mydf, aes(x= Names, y= More)) +
geom_bar(stat = "identity") 

I have a feeling that the problem lies with the way my data is organised, but I am not sure.

Answer 1

you need to change your data to long format where one column is for values and another for labels:

    Names values label
1   Sarah    8    less
2   Mark    13    less
3   Peter   11    less
1   Sarah    25    equal
2   Mark    13    equal
3   Peter   26    equal
1   Sarah    8    more
2   Mark    13    more
3   Peter   5    more

then the code will be

test <- ggplot(mydf, aes(x= label, y= values, fill=names)) +
  geom_bar(position="dodge",  stat="identity") 
test

here is an example: https://www.r-graph-gallery.com/48-grouped-barplot-with-ggplot2.html

Answer 2

You can use the data.table package to melt the data into long format.

library(data.table)

df <- melt(mydf, id.vars = "Names", variable.name = "category",
           value.name="scores")

If you want to have the grouped chart, you can specify position="dodge".

ggplot(df, aes(x = category , y= scores, fill = Names)) +
  geom_bar(position="dodge", stat = "identity")