Ingrid Tohver wrote:
I would like to run a t-test within a "by" group function. My
dataset, "error", is organized as the following (I have 133 Sites):
Site week Dataset Region lat_map long_map mean_tsim diff20 diff40
diff80
ALFI 15 USACE UC 48.15625 -117.0938 8.87 1.34 1.90
2.98
ALFI 16 USACE UC 48.15625 -117.0938 10.28 0.57 1.08
2.27
ALFI 17 USACE UC 48.15625 -117.0938 11.08 0.74 1.30
2.52
ALFI 18 USACE UC 48.15625 -117.0938 12.23 0.42 1.11
2.42
ALFI 19 USACE UC 48.15625 -117.0938 13.19 1.00 1.73
3.14
ALFI 20 USACE UC 48.15625 -117.0938 14.31 1.77 2.62
3.78
I am interested in running the t-test by the "Site" index. My code
looks like this:
t_test<-by(error, error['Site'], function(dat) t.test(subset(error
$diff20),subset(error$diff80), data=dat))
This code runs the t-test, but over the whole dataset without
discriminating by Site, so each Site's result is the same. Could
someone help determine a better approach or why mine is not working.
I guess you want
by(error, error['Site'], function(dat) t.test(dat$diff20, dat$diff40))
Uwe Ligges
Thank you,
Ingrid
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