stdev error

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 at sapo.pt>
Sent: Friday, March 11, 2022 9:24 AM
To: reichmanj at sbcglobal.net; r-help at 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


?s 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

   


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