R help - Oct 2012 - Mean Help

I have a dataframe.
Let's suppose that i have two columns. The first one contains height, the
second one contains eye color that can be Green, Blue or Brown.
I want to calculate the aritmetic mean of the height only for those people
who have Blue eyes. How can I do it?
Thank you for your availability.




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Thank you ... can you explain what you've done?



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Many forms, but I'll recommend this one this time around:

aggregate(height ~ eyes, DATA, mean)

See ?aggregate for an explanation of what aggregate() does and
?formula for an explanation of the tilde syntax.

Note that this assumes your column names are "height" and
"eyes."
Adjust as needed.

Michael

On Wed, Oct 31, 2012 at 1:18 PM, Hard Core <gioxc at hotmail.it>
wrote:
> I have a dataframe.
> Let's suppose that i have two columns. The first one contains height,
the
> second one contains eye color that can be Green, Blue or Brown.
> I want to calculate the aritmetic mean of the height only for those people
> who have Blue eyes. How can I do it?
> Thank you for your availability.
>
>
>
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Mean-Help-tp4648000.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

please provide a bit of the dataframe in the future using the dput() function
> x<-data.frame(height=1:10,
color=sample(c("blue","green","brown"),10,replace=T))
> x
   height color
1       1  blue
2       2 green
3       3  blue
4       4 brown
5       5  blue
6       6 brown
7       7 green
8       8 brown
9       9 green
10     10 brown
> blue.eyes <- x[x$color=="blue", ]
> blue.eyes
  height color
1      1  blue
3      3  blue
5      5  blue

should create a new dataframe with only those that have blue eyes, then
> mean(blue.eyes$height)
[1] 3

should provide you with the mean of those.

On 31.10.2012, at 14:18, Hard Core wrote:
> I have a dataframe.
> Let's suppose that i have two columns. The first one contains height,
the
> second one contains eye color that can be Green, Blue or Brown.
> I want to calculate the aritmetic mean of the height only for those people
> who have Blue eyes. How can I do it?
> Thank you for your availability.
> 
> 
> 
> 
> --
> View this message in context:
http://r.789695.n4.nabble.com/Mean-Help-tp4648000.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.