Thank you both, very much.

Using the identity function I() is a very nice trick, but it still feels
like a trick.

Using ggplot makes the most sense to me.
ggplot(df, aes(x=x, y=y, colour=factor(type))) +
       geom_point(size=1) +
       geom_smooth()

Thank you very much for taking the time to explain the syntax.

I had tried using the ggplot function, but I couldn't figure out how to
handle the"colour=factor(type)" part.
(my erroneous formulas are omitted for clarity)

On Tue, Jan 25, 2011 at 12:06 PM, Brian Diggs <diggsb@ohsu.edu> wrote:

> On 1/25/2011 9:44 AM, Felipe Carrillo wrote:
>
>> try this:
>> qplot(x, y, data=df, colour=factor(type), size=I(1)) + geom_smooth()
>>
>
> Felipe very nicely answered the "how" of your question.  I thought I'd
> followup with the "why."
>
> Using qplot, it assumes that you are giving a set of aesthetic mappings.
>  As such, size is being mapped to a variable that is 1 for all entries.
>  Then, in the usual way, a mapping is created between values of the variable
> in the data space and in the aesthetic space (actual sizes) and a legend is
> created to display this mapping.  Enclosing the 1 in an I() indicates that
> you are giving a literal value to set the aesthetic to, in which case no
> mapping between aesthetic and data space (nor legend) is needed.
>
> Alternatively, you can use an identity scale to state that the data and
> aesthetic spaces are the same, and tell it to not plot the legend.
>
>
> qplot(x, y, data=df, colour=factor(type), size=1) +
>        geom_smooth() +
>        scale_size_identity(legend=FALSE)
>
> The distinction between aesthetic mapping and setting is even more evident
> in ggplot notation:
>
> ggplot(df, aes(x=x, y=y, colour=factor(type))) +
>        geom_point(size=1) +
>
>        geom_smooth()
>
>
>  Felipe D. Carrillo
>> Supervisory Fishery Biologist
>> Department of the Interior
>> US Fish&  Wildlife Service
>> California, USA
>> http://www.fws.gov/redbluff/rbdd_jsmp.aspx
>>
>>
>>
>>
>> ----- Original Message ----
>>
>>> From: Gene Leynes<gleynes+r@gmail.com <gleynes%2Br@gmail.com>>
>>> To: r-help@r-project.org
>>> Sent: Tue, January 25, 2011 9:28:20 AM
>>> Subject: [R] ggplot - controlling point size
>>>
>>> Can anyone illuminate the following for me?
>>> How can I get rid of the blue line in the key in the second plot?
>>>
>>> ## Create a simple data frame
>>> df=data.frame(x=1:1000, y=2*1:1000+rnorm(1000,sd=1000),
>>>         type=sample(letters[1:2],1000, replace=TRUE))
>>>
>>> ## Very nice!  Almost what I want
>>> qplot(x, y, data=df, colour=factor(type)) + geom_smooth()
>>>
>>> ## Make a nicer plot, with smaller points
>>> ## but why does that add the little blue line with a 1?
>>> qplot(x, y, data=df, colour=factor(type), size=1) + geom_smooth()
>>>
>>
> --
> Brian S. Diggs, PhD
> Senior Research Associate, Department of Surgery
> Oregon Health & Science University
>

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