ggplot each group consists of only one observation

问题:

I'm trying to make a plot similar to this answer: https://stackoverflow.com/a/4877936/651779

My data frame looks like this:

df2 <- read.table(text='measurements samples value 1        4hours   sham1     6 2          1day   sham1   175 3         3days   sham1   417 4         7days   sham1   163 5        14days   sham1    37 6        90days   sham1   134 7        4hours   sham2     8 8          1day   sham2   402 9         3days   sham2   482 10        7days   sham2    67 11       14days   sham2    16 12       90days   sham2    31 13       4hours   sham3   185 14         1day   sham3   402 15        3days   sham3   482 16        7days   sham3    85 17       14days   sham3    29 18       90days   sham3    10',header=T) 

And plot it with

ggplot(df2, aes(measurements, value)) + geom_line(aes(colour = samples)) 

No lines show in the plot, and I get the message

geom_path: Each group consist of only one observation.  Do you need to adjust the group aesthetic? 

I don't see where what I'm doing is different from the answer I linked above. What should I change to make this work?

回答1:

Add group = samples to the aes of geom_line. This is necessary since you want one line per samples rather than for each data point.

ggplot(df2, aes(measurements, value)) +    geom_line(aes(colour = samples, group = samples)) 

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