How to plot min and max of two columns per row as a scatterplot

Question

I have a dataframe that looks something like this:

| id | length_bgn | length_end |
--------------------------------
| 1  |   209      |    215     |
| 2  |   324      |    125     |
| 3  |   167      |    156     |
| .. |   ...      |    ...     |
--------------------------------

I would like to make a scatterplot with the minimum of the length (per row) on the X-axis and the maximum per row on the Y axis. I have tried:

qplot(min(length_bgn, length_end), max(length_bgn, length_end), data=df)

However this plots a single point of the minimum of both columns against the maximum of both columns. Am I using the wrong functions? Or would it be better to manipulate the dataframe somehow? Please excuse any naivety, I am still quite new to R and ggplot2.

Any help would be much appreciated.

Edit: Example plot using the above code:

Answer 1

EDIT

library("ggplot2")

df <- read.table(text = " id  length_bgn  length_end 
        1     209          215     
 2     324          125     
 3     167          156     ", header=TRUE)

df$x <- apply(df[,c(2,3)], 1, min)
df$y <- apply(df[,c(2,3)], 1, max)


qplot(x, y, data=df)

Answer 2

@gauden's solution is good (to do the processing before plotting), but if you really want ggplot to do that work for you too, you can. [Using df that @gauden provided.]

qplot(pmin(length_bgn, length_end), pmax(length_bgn, length_end), data=df)