R help - Aug 2016 - add segments from other data ggplot

Dear Petr,

In your code:

p<-ggplot(ram.ag, aes(Raman, XRD, colour=mereni))
p+geom_point(size=5)+geom_segment(data=dat, aes(x=Ramanpuv,
y=XRDpuv,xend=Ramannov,
yend=XRDnov), arrow = arrow(length = unit(1,"cm")))

you have set mereni to control the colour aesthetic in the call to ggplot.
This will be used in all subsequent calls to geoms, unless you make a
local call to aes to override it. So both ram.ag and dat would require
mereni columns for this to work.

In the second piece of code you use a call to aes to override colour in
the call to geom_segment, which gets you past the error, but do not set it
to a variable in dat. You shouldn't set an aesthetic to a constant
("black"), use colour="black" outside of the aes() if you
want it set
(although it is redundant in this case, black being the default).

If you are using multiple data sources it is probably safer to refer to
them and set the appropriate aesthetics where they are used, e.g.

p <- ggplot()+geom_point(data=ram.ag,aes(x=Raman,y=XRD,colour=mereni))+
geom_segment(data=dat,aes(x=Ramanpuv,y=XRDpuv,xend=Ramannov,yend=XRDnov),ar
row=arrow(length=unit(1,"cm")))


Hope this helps, I apologise if it isn't very clear.

Regards,
Ron.

Thanks Ron.

Your explanation is clear, at least to me. I did not use the approach of start
with plain ggplot call following some geom calls before.

However I must say I finally turned back to standard graphics which seems to me
easier in this case and I can easily add other values without many problems. But
I keep your solution for future.

Thanks again

Petr
> -----Original Message-----
> From: Crump, Ron [mailto:R.E.Crump at warwick.ac.uk]
> Sent: Monday, August 15, 2016 12:57 PM
> To: PIKAL Petr <petr.pikal at precheza.cz>
> Cc: r-help at r-project.org
> Subject: Re: [R] add segments from other data ggplot
>
> Dear Petr,
>
> In your code:
>
> p<-ggplot(ram.ag, aes(Raman, XRD, colour=mereni))
> p+geom_point(size=5)+geom_segment(data=dat, aes(x=Ramanpuv,
> y=XRDpuv,xend=Ramannov,
> yend=XRDnov), arrow = arrow(length = unit(1,"cm")))
>
> you have set mereni to control the colour aesthetic in the call to ggplot.
> This will be used in all subsequent calls to geoms, unless you make a local
call
> to aes to override it. So both ram.ag and dat would require mereni columns
> for this to work.
>
> In the second piece of code you use a call to aes to override colour in the
call
> to geom_segment, which gets you past the error, but do not set it to a
> variable in dat. You shouldn't set an aesthetic to a constant
("black"), use
> colour="black" outside of the aes() if you want it set (although
it is redundant
> in this case, black being the default).
>
> If you are using multiple data sources it is probably safer to refer to
them and
> set the appropriate aesthetics where they are used, e.g.
>
> p <-
> ggplot()+geom_point(data=ram.ag,aes(x=Raman,y=XRD,colour=mereni))+
> geom_segment(data=dat,aes(x=Ramanpuv,y=XRDpuv,xend=Ramannov,yen
> d=XRDnov),ar
> row=arrow(length=unit(1,"cm")))
>
>
> Hope this helps, I apologise if it isn't very clear.
>
> Regards,
> Ron.

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