ggplot Error: similar data graphs, why not anymore? - r

Question

I am graphing some data with ggplot. However, I don't understand the error I'm getting with slightly different data than data that I can graph successfully. For example, this data graphs successfully:
to_graph <- structure(list(Teacher = c("BS", "BS", "FA"
), Level = structure(c(2L, 1L, 1L), .Label = c("BE", "AE", "ME",
"EE"), class = "factor"), Count = c(2L, 25L, 28L)), .Names = c("Teacher",
"Level", "Count"), row.names = c(NA, 3L), class = "data.frame")
ggplot(data=to_graph, aes(x=Teacher, y=Count, fill=Level), ordered=TRUE) +
geom_bar(aes(fill = Level), position = 'fill') +
scale_y_continuous("",formatter="percent") +
scale_fill_manual(values = c("#FF0000", "#FFFF00","#00CC00", "#0000FF")) +
opts(axis.text.x=theme_text(angle=45)) +
opts(title = "Score Distribution")
But this does not:
to_graph <- structure(list(School = c(84351L, 84384L, 84385L, 84386L, 84387L,
84388L, 84389L, 84397L, 84398L, 84351L, 84384L, 84385L, 84386L,
84387L, 84388L, 84389L, 84397L, 84398L, 84351L, 84386L), Level = structure(c(2L,
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 3L, 3L), .Label = c("BE", "AE", "ME", "EE"), class = "factor"),
Count = c(3L, 7L, 5L, 4L, 3L, 4L, 4L, 6L, 2L, 116L, 138L,
147L, 83L, 76L, 81L, 83L, 85L, 53L, 1L, 1L)), .Names = c("School",
"Level", "Count"), row.names = c(NA, 20L), class = "data.frame")
ggplot(data=to_graph, aes(x=School, y=Count, fill=Level), ordered=TRUE) +
geom_bar(aes(fill = Level), position = 'fill') +
scale_y_continuous("",formatter="percent") +
scale_fill_manual(values = c("#FF0000", "#FFFF00","#00CC00", "#0000FF")) +
opts(axis.text.x=theme_text(angle=90)) +
opts(title = "Score Distribution")
With the latter code, I get this error:
stat_bin: binwidth defaulted to range/30. Use 'binwidth = x' to adjust
this. Error in if (!all(data$ymin == 0)) warning("Filling not well
defined when ymin != 0") : missing value where TRUE/FALSE needed
Anyone know what's going on here? Thank you!

Answer 1

The error occurs because your x variable has numerical values, when in reality you want them to be discrete, i.e. use x=factor(School).
The reason for this is that stat_bin, the default stat for geom_bar, will try to summarise for each unique value of x. When your x-variable is numeric, it tries to summarise at each integer in the range. This is clearly not what you need.
ggplot(data=to_graph, aes(x=factor(School), y=Count, fill=Level), ordered=TRUE) +
geom_bar(aes(fill = Level), position='fill') +
opts(axis.text.x=theme_text(angle=90)) +
scale_y_continuous("",formatter="percent") +
opts(title = "Score Distribution") +
scale_fill_manual(values = c("#FF0000", "#FFFF00","#00CC00", "#0000FF"))