stdev error

Hallo

with(my_tbl, aggregate(Bse_bwt, list(Cat), function(x) c(n=length(x), mean=mean(x), st_dev=sd(x))))

Or am I missing something?

Cheers
Petr


-----Original Message-----
From: R-help <r-help-bounces at r-project.org> On Behalf Of Chris Evans
Sent: Friday, March 11, 2022 3:22 PM
To: reichmanj at sbcglobal.net
Cc: r-help at r-project.org
Subject: Re: [R] stdev error

Can't see your data but perhaps:

my_tbl %>%
  mutate(Bse_bwt = round(Bse_bwt * 2) / 2) %>%
  group_by(Cat, Bse_bwt) %>%
  summarize(count = n(),
     Bse_ftv = mean(Bse_ftv),
     stdev = if_else(count > 1,
                     sd(Bse_ftv),
                     NA_real_))


----- Original Message -----

From: "Jeff Reichman" <reichmanj at sbcglobal.net>
To: r-help at r-project.org
Sent: Friday, 11 March, 2022 15:14:52
Subject: [R] stdev error

r-help forum



When I run the following code



my_tbl %>%

 mutate(Bse_bwt = round(Bse_bwt * 2) / 2) %>%

 group_by(Cat, Bse_bwt) %>%

 summarize(count = n(), Bse_ftv = mean(Bse_ftv), stdev = sd(Bse_ftv))



I get the following error:



Error: `stdev` refers to a variable created earlier in this summarise().

Do you need an extra mutate() step?



I suspect it is because the standard deviation of a length-one vector
is NA and R is errorerrors out on the standard deviation  of 1. So
then I tried



summarize(count = n(), Bse_ftv = mean(Bse_ftv), stdev = if(n()>1)
sd(Bse_ftv) else 0) and this didn't seem to work either. So there has
to be a way to add some sort of error checker to my standard deviation
function to check if n > 1 and then take the standard deviation in dplyr.



Jeff




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Chris Evans (he/him) <chris at psyctc.org> Visiting Professor, UDLA, Quito, Ecuador & Honorary Professor, University of Roehampton, London, UK.
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