R help - Aug 2007 - a new-bie question about obtaining certain value from the print out

Hi everyone,

I am quite new to R.

my command is
t.test(c(1:5,7:11), y=c(1:10),alternative = c("two.sided"), paired =
TRUE)

The output is

        Paired t-test

data:  c(1:5, 7:11) and c(1:10)
t = 3, df = 9, p-value = 0.01496
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
 0.1229738 0.8770262
sample estimates:
mean of the differences
                    0.5
According to the reference:

Value
A list with class "htest" containing the following components:
p.value the p-value for the test.

How can I get only the p.value as the output instead of the whole print out?

Thanks a lot!

-Kurt

You need to save the output in order to do something with it (the
default if you don't save the output is to call the print method, so
what you are seeing is the results of calling print.htest on the return
value from t.test).

Save the output by doing something like:
> out <- t.test(c(1:5,7:11), y=c(1:10), 
+ alternative = c("two.sided"), paired = TRUE)

Now the results are stored in "out" (or whatever better name you come
up
with)

To access the p-value you can do:
> out$p.value
Or use that in another expression.

The details on what comes after the '$' can be found in this case from
the t.test help page, or in general using the str function:
> str(out)
Gives a wealth of information (sometimes too much) on the components of
the returned object.

Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at intermountainmail.org
(801) 408-8111
 
 
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of kurt Zhao
> Sent: Wednesday, August 29, 2007 2:53 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] a new-bie question about obtaining certain value 
> from the printout
> 
> Hi everyone,
> 
> I am quite new to R.
> 
> my command is
> t.test(c(1:5,7:11), y=c(1:10),alternative = c("two.sided"), 
> paired = TRUE)
> 
> The output is
> 
>         Paired t-test
> 
> data:  c(1:5, 7:11) and c(1:10)
> t = 3, df = 9, p-value = 0.01496
> alternative hypothesis: true difference in means is not equal to 0
> 95 percent confidence interval:
>  0.1229738 0.8770262
> sample estimates:
> mean of the differences
>                     0.5
> According to the reference:
> 
> Value
> A list with class "htest" containing the following components:
> p.value the p-value for the test.
> 
> How can I get only the p.value as the output instead of the 
> whole print out?
> 
> Thanks a lot!
> 
> -Kurt
> 
> ______________________________________________
> R-help at stat.math.ethz.ch 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.
>

On 30/08/2007, at 8:53 AM, kurt Zhao wrote:
> Hi everyone,
>
> I am quite new to R.
>
> my command is
> t.test(c(1:5,7:11), y=c(1:10),alternative = c("two.sided"),
paired
> = TRUE)
>
> The output is
>
>         Paired t-test
>
> data:  c(1:5, 7:11) and c(1:10)
> t = 3, df = 9, p-value = 0.01496
> alternative hypothesis: true difference in means is not equal to 0
> 95 percent confidence interval:
>  0.1229738 0.8770262
> sample estimates:
> mean of the differences
>                     0.5
> According to the reference:
>
> Value
> A list with class "htest" containing the following components:
> p.value the p-value for the test.
>
> How can I get only the p.value as the output instead of the whole  
> print out?

t.test(c(1:5,7:11), y=c(1:10),alternative = c("two.sided"), paired =  
TRUE)$p.value

Or:

rslt <- t.test(c(1:5,7:11), y=c(1:10),alternative = c("two.sided"),
paired = TRUE)
rslt$p.value

Look at names(rslt) and/or str(rstl) to see what else you can dig out.

A side-comment:  You ***do not need*** the c() wrappers for 1:10 and  
"two.sided";
the c() function is for ``combine'' or ``catenate''.  You
don't need
to ``combine'' a single
item!  The wrapper does no harm, but it's a waste of key strokes and  
indicates a certain
lack of insight which *could* do harm in more complex situations.

			cheers,

				Rolf Turner

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