“ group =”变量在data.frame（）中的工作原理

Question

I can't find much information on exactly how the group variable in data.frame functions. I have three vectors as follows:

compare <- c("5vs2", "8vs5", "11vs8")
up <- c(4432, 1578, 2254)
down <- c(-4360, -1324, -2652)

and I am trying to create a data frame for a bar chart. I have created it as follows:

up_down <- data.frame(
  group = c("Up", "Down"),
  x = compare, 
  y=c(up, down))

The output dataframe is as follows:

  group     x     y
1    Up  5vs2  4432
2  Down  8vs5  1578
3    Up 11vs8  2254
4  Down  5vs2 -4360
5    Up  8vs5 -1324
6  Down 11vs8 -2652

It can be seen here that in row 5, the grouping should be Down but instead it has made it Up . What exactly am I missing here?

Upon plotting the chart, the x values are then placed out of order, with the 11vs8 being put first, the 6vs3 second and the 9vs6 last. I feel like these should be obvious problems to solve but I can't figure them out.

ggplot(up_down, aes(x=x, y=y, fill=group))+
  geom_bar(stat="identity", position="identity")

Answer 1

You're binding vectors of lengths 2, 3, and 6. R recycles vectors to fit the largest length, so group is repeated 1 2 1 2 1 2 . If you want to avoid that here, try instead: group = rep(c("Up", "Down"), each = 3)