Julio Diaz Julio Diaz - 2 months ago 13
R Question

Order Bars in ggplot2 bar graph

I am trying to make a bar graph where the largest bar would be nearest to the y axis and the shortest bar would be furthest. So this is kind of like theTable I have

Name Position
1 James Goalkeeper
2 Frank Goalkeeper
3 Jean Defense
4 Steve Defense
5 John Defense
6 Tim Striker


So I am trying to build a bar graph that would show the number of players according to position

p <- ggplot(theTable, aes(x = Position)) + geom_bar(binwidth = 1)


but the graph shows the goalkeeper bar first then the defense, and finally the striker one. I would want the graph to be ordered so that the defense bar is closest to the y axis, the the defense one, and finally the striker one.
Thanks

Answer

The key with ordering is to set the levels of the factor in the order you want; an ordered factor is not required, the extra information in an ordered factor isn't necessary and if these data are being used in any statistical model, the wrong parametrisation might result - polynomial contrasts aren't right for nominal data such as this.

## set the levels in order we want
theTable <- within(theTable, 
                   Position <- factor(Position, 
                                      levels=names(sort(table(Position), 
                                                        decreasing=TRUE))))
## plot
ggplot(theTable,aes(x=Position))+geom_bar(binwidth=1)

barplot figure

In the most general sense, we simply need to set the factor levels to be in the desired order. There are multiple ways of doing this depending on the situation. For instance, we could do:

levels(theTable$Position) <- c(...)

and simply list the levels in the desired order on the right hand side. You can also specify the level order within the call to factor as above:

theTable$Position <- factor(theTable$Position, levels = c(...))