[R] stdev error

[Rui Barradas]

Hello,

Yes, you're right.
Thanks for posting this, in my original post unlike what I thought I was 
able to reproduce the error. All stdev values were NA when in fact after 
changing the mean to hp1 = mean(hp) some of them are not, there are 
zeros in the output column stdev.

Rui Barradas

Às 17:49 de 11/03/2022, Jeff Reichman escreveu:
> Rui
> 
> Found my problem, or at least I think I found the problem.
> 
> # BEWARE: reusing variables may lead to unexpected results - https://dplyr.tidyverse.org/reference/summarise.html
> 
> I changed my variable name  and problem resolved.
> 
> Jeff
> 
> -----Original Message-----
> From: Rui Barradas <ruipbarradas using sapo.pt>
> Sent: Friday, March 11, 2022 9:24 AM
> To: reichmanj using sbcglobal.net; r-help using r-project.org
> Subject: Re: [R] stdev error
> 
> Hello,
> 
> I cannot reproduce this error with a built-in data set.
> Can you post str(my_tbl)?
> 
> 
> suppressPackageStartupMessages(library(dplyr))
> 
> mtcars %>%
>     mutate(hp = round(hp * 2) / 2) %>%
>     group_by(cyl, hp) %>%
>     summarise(
>       count = n(),
>       hp = mean(hp),
>       stdev = sd(hp)
>     )
> #> `summarise()` has grouped output by 'cyl'. You can override using the `.groups` #> argument.
> #> # A tibble: 23 x 4
> #> # Groups:   cyl [3]
> #>      cyl    hp count stdev
> #>    <dbl> <dbl> <int> <dbl>
> #>  1     4    52     1    NA
> #>  2     4    62     1    NA
> #>  3     4    65     1    NA
> #>  4     4    66     2    NA
> #>  5     4    91     1    NA
> #>  6     4    93     1    NA
> #>  7     4    95     1    NA
> #>  8     4    97     1    NA
> #>  9     4   109     1    NA
> #> 10     4   113     1    NA
> #> # ... with 13 more rows
> 
> Hope this helps,
> 
> Rui Barradas
> 
> 
> Às 14:14 de 11/03/2022, Jeff Reichman escreveu:
>> 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
>>
>>    
>>
>>
>> 	[[alternative HTML version deleted]]
>>
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>