Adding diagonal line to a twoway graph when axes have very different ranges

[James Sanders]

Dear StataList,
I am trying to add a diagonal line to a twoway graph in which the x and y axes have very different ranges. For example,

sysuse auto, clear
twoway (scatter price length)

When I use the function y=x option with the y axis as the range value, the x axis is extended and the line begins at the lowest observed value on the y axis:

sysuse auto, clear
twoway (scatter price length) (function y=x, range(price))

Switching away from function to line produces essentially the same graph:

sysuse auto, clear
twoway (scatter price length) (line price price, sort)

Is there a way to keep both axes as they originally are but add a diagonal line that extends from (0,0) to the upper right quadrant?

Thank you.

[Friedrich Huebler]

Replace price by length in your second example.

sysuse auto, clear
twoway (scatter price length) (function y=x, range(length))

Edit: I misunderstood your question. I think you want something like this:

twoway (scatter price length) (scatteri 0 140 16000 240, connect(l) msymbol(i))

[James Sanders]

Thank you for your help Friedrich.