Formatting data for ggplot2

References

Create a demo data

datWide <- read.table(header = TRUE, text = "
n       A       B
10      0.5     0.6
100     0.35    0.4
1000    0.27    0.3
")

Plot as is

library(ggplot2)
ggplot(data = datWide) +
    layer(geom = "line", mapping = aes(x = n, y = A), color = "red") +
    layer(geom = "line", mapping = aes(x = n, y = B), color = "blue") +
    layer(geom = "point", mapping = aes(x = n, y = A)) +
    layer(geom = "point", mapping = aes(x = n, y = B)) +
    theme_bw() +
    theme(legend.key = element_blank())

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Transform data to long format

library(reshape2)
datLong <- melt(data          = datWide,
              id.vars       = c("n"),
              measure.vars  = c("A","B"),
              variable.name = "variable",
              value.name    = "value")
datLong

##      n variable value
## 1   10        A  0.50
## 2  100        A  0.35
## 3 1000        A  0.27
## 4   10        B  0.60
## 5  100        B  0.40
## 6 1000        B  0.30

Plot using the long format data

ggplot(data = datLong,
       mapping = aes(x = n, y = value, color = variable)) +
           layer(geom = "point") +
           layer(geom = "line") +
           scale_color_discrete(name = "") + 
           theme_bw() +
           theme(legend.key = element_blank())

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