new2R new2R - 1 month ago 13
R Question

how to add layers in ggplot using a for-loop

I would like to plot each column of a dataframe to a separate layer in ggplot2.
Building the plot layer by layer works well:

df<-data.frame(x1=c(1:5),y1=c(2.0,5.4,7.1,4.6,5.0),y2=c(0.4,9.4,2.9,5.4,1.1),y3=c(2.4,6.6,8.1,5.6,6.3))

ggplot(data=df,aes(df[,1]))+geom_line(aes(y=df[,2]))+geom_line(aes(y=df[,3]))


Is there a way to plot all available columns at ones by using a single function?

I tried to do it this way but it does not work:

plotAllLayers<-function(df){
p<-ggplot(data=df,aes(df[,1]))
for(i in seq(2:ncol(df))){
p<-p+geom_line(aes(y=df[,i]))
}
return(p)
}

plotAllLayers(df)

Answer

One approach would be to reshape your data frame from wide format to long format using function melt() from library reshape2. In new data frame you will have x1 values, variable that determine from which column data came, and value that contains all original y values.

Now you can plot all data with one ggplot() and geom_line() call and use variable to have for example separate color for each line.

 library(reshape2)
 df.long<-melt(df,id.vars="x1")
 head(df.long)
  x1 variable value
1  1       y1   2.0
2  2       y1   5.4
3  3       y1   7.1
4  4       y1   4.6
5  5       y1   5.0
6  1       y2   0.4
 ggplot(df.long,aes(x1,value,color=variable))+geom_line()

enter image description here

If you really want to use for() loop (not the best way) then you should use names(df)[-1] instead of seq(). This will make vector of column names (except first column). Then inside geom_line() use aes_string(y=i) to select column by their name.

plotAllLayers<-function(df){
  p<-ggplot(data=df,aes(df[,1]))
  for(i in names(df)[-1]){ 
    p<-p+geom_line(aes_string(y=i))
  }
  return(p)
}

plotAllLayers(df)

enter image description here

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