Imri wrote:
Thanks for the answer, but it's still don't work.

What I get for each genotype look like this:

$`02-02`

        Welch Two Sample t-test

data: slength[, 6] by slength[, 3]

You can't get that if you did what I said...


t = 1.6262, df = 682.116, p-value = 0.1044
alternative hypothesis: true difference in means is not equal to 0 95 percent confidence interval: -0.1336494 1.4224993 sample estimates: mean in group d mean in group w 2.419450 1.775025
 For each of the  genotypes all the data is tests, not just the data for the
unique genotype.

Peter Dalgaard wrote:
Imri wrote:
My data (slength) look like this:
Plant Block Treat Genotype Source MPH
1       1     1     w   05-AZM sp 160            NA
2       2     1     w    12-50    463            NA
3       3     1     w    12-51 sp 150     0.0508982
4       5     1     w    29-42    567     0.9017094
5       6     1     w  KNG-KNG    811            NA
6       7     1     w    02-02      1            NA

Treat column has w or d for each Plant(row). I wont to do t.test of
MPH~Treat for each of the genotypes (128 total). I tried :

t.tests<-by(slength, slength[,4], function(x)
t.test(slength[,6]~slength[,3]))
but it is not what I need.
Do you have any ideas?
  Thanks
         Imri
Your function(x)... doesn't depend on x! Try

...t.test(MPH~Treat, data=x)

--
    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalga...@biostat.ku.dk)              FAX: (+45) 35327907

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--
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalga...@biostat.ku.dk)              FAX: (+45) 35327907

______________________________________________
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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.

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