geom_segment

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Hi guys,

I am studying ggplot2 from R graphics cookbook(

3.10 Making a Cleveland Dot Plot ,https://r-graphics.org/recipe-bar-graph-dot-plot), if I use the code :

ggplot(tophit, aes(x = avg, y = name)) +

   geom_segment(aes(yend = name),xend=0) 

the plot looks like in upper panel in attachment., this is what i want  otherwise,

when the code:

ggplot(tophit, aes(x = avg, y = name)) +

   geom_segment(aes(yend = name,xend=0))

the plot looks like lower panel. this is a bad thing.

 I am wondering about  if xend put in aes ,x-axis sort of starts from 3.0. xend put outside the aes, the x-axis  starts from 0.

who could expain it?

many thanks!