Question

I want to plot a bunch of variables against each other by using a loop and par(ask=T) to just update the plot after each mouse click.

The following code works fine using the plot() function:

require(ggplot2)
df1 <- data.frame(id=seq(1,10,1)
    ,col1 = runif(10)
    ,col2 = runif(10)
    ,col3 = runif(10)
    ,col4 = runif(10)
    ,col5 = runif(10)
    ,col6 = runif(10)
    ,col7 = runif(10)
    ,col8 = runif(10)
    ,col9 = runif(10)
    ,col10 = runif(10)
    )

par(ask=TRUE)
for(i in 2:9){
colName2 <- paste("col",i,sep="")
plot(df1$col1, df1[,colName2])
flush.console()
}
par(ask=FALSE)

However if I run the same code and use qplot() instead of plot(), the plot window never updates.

Any ideas why or workarounds?

Answer 1

ggplot2 graphs are not displayed just by a call to qplot (or ggplot); when the value returned by this function is printed (as it is by default when issued on the command line), then the plot is drawn. Within a loop, the return value of a function is not printed by default, so nothing is shown. Explicitly print it, and it will show up.

This is covered in R FAQ 7.22.

par(ask=TRUE)
for(i in 2:9){
  colName2 <- paste("col",i,sep="")
  print(qplot(df1$col1, df1[,colName2]))
  flush.console()
}
par(ask=FALSE)