R/ggplot2: is it possible to boxplot columns from a dataframe without a factor column?

Question

Struggling a little with ggplot here. As the title says: is it possible to boxplot columns from a dataframe without a factor column? That is to say, using names of columns of interest as x?

Example 1 (graphics)

df <- data.frame(c(0.2, 0.3, 0.4), c(0.4, 0.2, 0.5))
colnames(df) <- c("A1", "A2")
rownames(df) <- c("001", "002", "003")
df

     A1  A2
001 0.2 0.4
002 0.3 0.2
003 0.4 0.5

boxplot(df[,"A1"], df[,"A2"], names=colnames(df))

Exemple 2 (ggplot2)

library(ggplot2)

df2 <- data.frame(c("A1", "A1", "A1", "A2", "A2", "A2"), c(0.2, 0.3, 0.4, 0.4, 0.2, 0.5))
colnames(df2) <- c("Series", "Value")
df2

  Series Value
1     A1   0.2
2     A1   0.3
3     A1   0.4
4     A2   0.4
5     A2   0.2
6     A2   0.5

p <- ggplot(df2, aes(as.factor(Series), Value)) + geom_boxplot()
p

In the second case, I lose the rownames that cannot be duplicated, although they're IDs I need to keep. So could I obtain this result with ggplot2 keeping the first data structure? Thanks

You'll have to process the first structure to obtain the second. ggplot(reshape2::melt(df), aes(x = variable, y = value)) + geom_boxplot() — d.b
– d.b, Commented Aug 14, 2019 at 18:14
Thanks, I've come across this syntax but I don't quite understand where do "value" and "variable" come from, and when I try to apply it to my actual data I get an "object 'variable' not found" error. data_to_plot <- my_data[, c("IC.2", "IC.3", "IC.4")] ggplot(reshape2::melt(data_to_plot), aes(x = variable, y = value)) + geom_boxplot() Using IC.2, IC.3, IC.4 as id variables Error in FUN(X[[i]], ...) : object 'variable' not found — rioualen
– rioualen, Commented Aug 14, 2019 at 18:28
I'm expecting reshape2::melt(df)to output something like the validated anwser here but it still shows my 3-column data, although it should group all values into 1 column, right? — rioualen
– rioualen, Commented Aug 14, 2019 at 18:59

rioualen · Accepted Answer · 2019-08-14 21:31:52Z

1

So I couldn't get reshape2 to work, however I came up with a solution using the tidyr package:

library(dplyr)
library(tidyr)
library(ggplot2)

df <- data.frame(c(0.2, 0.3, 0.4), c(0.4, 0.2, 0.5))
colnames(df) <- c("A1", "A2")
rownames(df) <- c("001", "002", "003")
df
    A1  A2
001 0.2 0.4
002 0.3 0.2
003 0.4 0.5

tidy_df <- df %>% gather(variable, value, c("A1", "A2"))
p <- ggplot(tidy_df, aes(x = variable, y = value)) + geom_boxplot()
p

answered Aug 14, 2019 at 21:31

rioualen

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