Set layers in ggplot2 via loop

Question

I would expected that

data <- data.frame(col1 = c(1, 2, 2, 3, 3, 4),
                   col2 = c(1, 2, 2, 1, 2, 1),
                   z = rnorm(6))
p1<-ggplot(data, aes(x=col1))

for(idx in unique(data$col2)){
    p1<-p1 + geom_bar(subset = .(col2 == idx), aes(y = ..count..),fill = "blue", alpha = 0.2)
}
p1

have the same output like

p1<-ggplot(data, aes(x=col1))
p1<-p1 + geom_bar(subset = .(col2 == 1), aes(y = ..count..),fill = "blue", alpha = 0.2)
p1<-p1 + geom_bar(subset = .(col2 == 2), aes(y = ..count..),fill = "blue", alpha = 0.2)
p1

but it istn't. So how could I produce in the for loop the same output like in the second example.

What kind of plot are you looking for? Your working example does not make sense to me. — Thierry
– Thierry, Commented Aug 26, 2013 at 13:11
I'm thinking he can make the plot without explicitly subsetting the data — Pete
– Pete, Commented Aug 26, 2013 at 13:16
Thierry iam speaking about a principle @Pete I know for example if I would melt the data frame by col2. But I am interrested doing this by for loop or any other loop to have the result if I would write the sequenz explicte like in the first example. — Klaus
– Klaus, Commented Aug 26, 2013 at 13:28
Subset the data yourself inside the loop - your loop doesn't work because idx == 2 at the end and that's what both layers will see. — hadley
– hadley, Commented Aug 26, 2013 at 14:12
@hadley, I know but I dont understand the this behavior, because for me the code in the loop looks like I would add in each step a knew layer. — Klaus
– Klaus, Commented Aug 26, 2013 at 14:55

hadley · Accepted Answer · 2013-08-27 16:12:08Z

2

This problem is simple if you do the subsetting yourself:

library(ggplot2)
data <- data.frame(
  col1 = c(1, 2, 2, 3, 3, 4),
  col2 = c(1, 2, 2, 1, 2, 1),
  z = rnorm(6))
ids <- unique(data$col2)

p1 <- ggplot(data, aes(col1, y = ..count..))

for(id in ids){
  df <- data[data$col2 == id, ]
  p1 <- p1 + geom_bar(data = df, fill = "blue", alpha = 0.2)
}
p1

answered Aug 27, 2013 at 16:12

hadley

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1 Comment

Klaus Over a year ago

Many thx. This was exactly what I tried before but it doesnt worked till now.

p1 <- ggplot(data, aes(x=col1)) df<-split(data, data$col2) for(i in df){    p1 <- p1 + geom_bar(data = i, aes(y = ..count..), fill = "blue", alpha = 0.2) } p1

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