R parallel coordinate plot with fixed scale on X-axis, no matter how large the plot becomes

问题

I am trying to build a parallel coordinate diagram in R for showing the difference in ranking in different age groups. And I want to have a fixed scale on the Y axis for showing the values.

Here is a PC plot :

The goal is to see the slopes of the lines really well. So if I have value 1 that is bound with the value 1000, I want to see the line going aaall the way down steeply.

In R so far, if I have values that are too big, my plot is all squished so everything fits and it's hard to visualize anything.

My code for drawing the parallel coordinate plot is the following so far:

pc_18_34 <- read.table("parCoordData_18_24_25_34.csv", header=FALSE, sep="\t")
#name columns of data frame
colnames(pc_18_34) = c("18-25","25-34")

#build the parallel coordinate plot
# doc : http://docs.ggplot2.org/current/geom_path.html
group <- rep(c("Top 10", "Top 10-29", "Top 30-49"), each = 18)
df <- data.frame(id = seq_along(group), group, pc_18_34[,1], pc_18_34[,2])
colnames(df)[3] = "18-25"
colnames(df)[4] = "25-34"
library(reshape2) # for melt

dfm <- melt(df, id.var = c("id", "group"))
dfm[order(dfm$group,dfm$ArtistRank,decreasing=TRUE),]
colnames(dfm)[3] = "AgeGroup"
colnames(dfm)[4] = "ArtistRank"

ggplot(dfm, aes(x=AgeGroup, y=ArtistRank, group = id, colour = group), main="Tops across age groups")+  geom_path(alpha = 0.5, size=1) + geom_path(aes(color=group))

I have looked into how to get the scales to change in ggplot, using libraries like scales but when I had a layer of scale, the diagram doesn't even show up anymore.

Any thoughts on how to make to use a fixed scale (say difference of 1 in rank shown as 5px in the plot), even if it means that the plot is very tall ?

Thaanks !! :)

回答1:

You can set the panel height to an absolute size based on the number of axis breaks. Note that the device won't scale automatically, so you'll have to adjust it manually for your plot to fit well.

library(ggplot2)
library(gtable)

p <- ggplot(Loblolly, aes(height, factor(age))) +
  geom_point()

gb <- ggplot_build(p)
gt <- ggplot_gtable(gb)
n <- length(gb$panel$ranges[[1]]$y.major_source)

# locate the panel in the gtable layout
panel <- gt$layout$t[grepl("panel", gt$layout$name)]
# assign new height to the panels, based on the number of breaks
gt$heights[panel] <- list(unit(n*25,"pt"))
grid.newpage()
grid.draw(gt)

来源：https://stackoverflow.com/questions/23906277/r-parallel-coordinate-plot-with-fixed-scale-on-x-axis-no-matter-how-large-the-p