[R] t.test data in one column

Phil Spector spector at stat.berkeley.edu
Thu Apr 1 21:04:33 CEST 2010

```Marlin -
Consider the following:

> df = data.frame(x=rep(1:4,2),y=rep(c('M','F'),c(2,2)))
> t.test(x~y,data=df)

Welch Two Sample t-test

data:  x by y
t = 4.899, df = 6, p-value = 0.002714
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
1.001052 2.998948
sample estimates:
mean in group F mean in group M
3.5             1.5

If you're uncomfortable with the formula notation, try

with(df,t.test(x[y=='M'],x[y=='F']))

- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spector at stat.berkeley.edu

On Thu, 1 Apr 2010, Marlin Keith Cox wrote:

> I need a two sample t.test between M and F.  The data are arranged in one
> column, x.  Cant seem to figure how to run a two sample t.test.  Not really
> sure what this output is giving me, but there should be no difference
> between M and F in the example, but summary p-value indicates this.
>
> How can I run a two sample t.test with data in one column.
>
> x=rep(c(1,2,3,4),2)
> y=rep(c("M","M","M","M","F","F","F","F"))
> data<-cbind(x,y)
> t.test(x,by=list(y))
> Thank you ahead of time.
> keith
>
>
>
> --
> M. Keith Cox, Ph.D.
> Alaska NOAA Fisheries, National Marine Fisheries Service
> Auke Bay Laboratories
> 17109 Pt. Lena Loop Rd.
> Juneau, AK 99801
> Keith.Cox at noaa.gov
> U.S. (907) 789-6603
>
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