Exchanging the axes in gnuplot

Question

I have been wondering about this for a while, and it might already be implemented in gnuplot but I haven't been able to find info online.

When you have a data file, it is possible to exchange the axes and assign the "dummy variable", say x, (in gnuplot's help terminology) to the vertical axis:

plot "data" u 1:2 # x goes to horizontal axis, standard
plot "data" u 2:1 # x goes to vertical axis, exchanged axes

However, when you have a function, you need to resort to a parametric function to do this. Imagine you want to plot x = y² (as opposite to y = x²), then (as far as I know) you need to do:

set parametric
plot t**2,t

which works nicely in this case. I think however that a more flexible approach would be desirable, something like

plot x**2 axes y1x1 # this doesn't work!

Is something like the above implemented, or is there an easy way to use y as dummy variable without the need to set parametric?

Answer 1

So here is another ugly, but gnuplot-only variant: Use the special filename '+' to generate a dynamic data set for plotting:

plot '+' using ($1**2):1

The development version contains a new feature, which allows you to use dummy variables instead of column numbers for plotting with '+':

plot sample [y=-10:10] '+' using (y**2):(y)

I guess that's what come closest to your request.

Answer 2

From what I have seen, parametric plots are pretty common in order to achieve your needs. If you really hate parametric plots and you have no fear for a VERY ugly solutions, I can give you my method...

My trick is to use a data file filled with a sequence of numbers. To fit your example, let's make a file sq with a sequence of reals from -10 to 10 :

seq -10 .5 10 > sq

And then you can do the magic you want using gnuplot :

plot 'sq' u ($1**2):($1)

And if you uses linux you can also put the command directly in the command line :

plot '< seq -10 .5 10' u ($1**2):($1)  

I want to add that I'm not proud of this solution and I'd love the "axis y1x1" functionality too.