Line Plot subset data with ggplot2 (facet)

Question

I have test score data. I want ggline plot for 3 different test scores in reading over various years (3 lines). I would like this stacked over 4 different test scores in writing the same years (4 lines). Having all 7 on one plot is confusing to read. I can subset the data so it shows either reading or writing, but I can't seem to stack them over top of each other neatly.

year, ID, test, score , type

2010, 1, R1, 72.75, R
2010, 1, R2, 68.25, R
2010, 1, R3, 83.75, R
2010, 1, W1, 89.25, W
2010, 1, W2, 58.25, W
2010, 1, W3, 64.25, W
2010, 1, W4, 90.25, W
2011, 1, R1, 52.25, R
2011, 1, R2, 90.25, R
2011, 1, R3, 73.25, R
2011, 1, W1, 79.5, W
2011, 1, W2, 89.25, W
2011, 1, W3, 85.25, W
2011, 1, W4, 78.25, W

…

I have this code to produce one graph with just reading:

ggplot(subset(df,skill %in% c("R1", "R2", "R3"))) + 
  geom_line(aes(year, score, group=skill, colour=skill))

I have tried to do this to get both, but it obviously is incorrect:

p1 <- subset(df,skill %in% c("R1", "R2", "R3"))
p2 <- subset(df,skill %in% c("W1", "W2", "W3", "W4"))
ggplot()+ geom_line(data=p1, aes(year, score, group=skill, colour=skill)) +
  geom_line(data=p2, aes(year, score, group=skill, colour=skill)) +
  facet_grid(~type)

Any help would be greatly appreciated

Your example data has a column `test` but your code is referring to a column `skill` which is not in your example data. Please use `dput(df))` and copy the output to your question so that it is easier for people to work with the data as you have it. See https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example — Eric Watt, Dec 11 '17 at 16:49
Try changing your plot code to use the whole dataset ("df") in a single `geom_line` layer plus the facets rather than having a separate `geom_line` layer per subset. — aosmith, Dec 11 '17 at 16:51

Eric Watt · Accepted Answer · 2017-12-11T17:15:03.983

If you're going to facet based on type, you don't need to subset the data into p1 and p2.

ggplot(df) + 
  geom_line(aes(year, score, group = skill, colour = skill)) +
  facet_wrap(~type)

Alternative, adding nrow =2 to stack the plots and scales = "free" to give them independent axes.

ggplot(df) + 
  geom_line(aes(year, score, group = skill, colour = skill)) +
  facet_wrap(~type, nrow = 2, scales = "free")

However, your comment says

This does work but it puts the graph side by side instead of stacked vertically. Is there a way to stack them one on top of the other and perhaps separate the legend so reading and writing are separate?

To address the separate legend, I would make each plot, and then combine using the package cowplot. Other ways to do this using gridExtra but cowplot makes this simple.

p1 <- ggplot(subset(df,skill %in% c("R1", "R2", "R3"))) + 
  geom_line(aes(year, score, group = skill, colour = skill)) +
  facet_wrap(~type, scales = "free")

p2 <- ggplot(subset(df,type %in% c("W"))) + 
  geom_line(aes(year, score, group = skill, colour = skill)) +
  facet_wrap(~type, scales = "free")

cowplot::plot_grid(p1, p2, nrow = 2)

thank you Eric for your response. This does work but it puts the graph side by side instead of stacked vertically. Is there a way to stack them one on top of the other and perhaps separate the legend so reading and writing are separate? — user9084595, Dec 11 '17 at 17:03

Line Plot subset data with ggplot2 (facet)

1 Answers1