[R] variable (column) in a data frame

[John Kane]

This seems more or less correct to me.

1> sum(df$a==1)
[1] 1
1> sum(df$a==2)
[1] 1
1> sum(df$aaa==2)
[1] 0

There is no df$aaa so the length is 0 which is what I think you are asking.
What am I missing?


John Kane
Kingston ON Canada


> -----Original Message-----
> From: paulo.barata at ensp.fiocruz.br
> Sent: Sun, 15 Jul 2012 11:30:37 -0300
> To: r-help at r-project.org
> Subject: [R] variable (column) in a data frame
> 
> 
> To the R help list,
> 
> When using a data frame, there is no warning or error message
> when I refer to a non-existent variable inside the data frame.
> 
> Example:
> 
> ##----------------------------------------------
> 
> a <- c(1,2,3)
> b <- c(11,22,33)
> df <- data.frame(a,b)
> df
> 
> ## correct: there is a column in df named 'a'
> ## the sum is correctly performed
> sum(df$a==2)
> 
> ## incorrect: there is no column in df named 'aaa',
> ## but the sum is performed anyway without either warning or error
> sum(df$aaa==2)
> 
> ##----------------------------------------------
> 
> Is there some way to make R issue either a warning or an error
> message in such a situation?
> 
> I am using R version 2.15.1 64-bit on Windows 7 Professional.
> 
> Thank you very much.
> 
> Paulo Barata
> 
> ---------------------------------------------------------------------
> Paulo Barata
> 
> ENSP - Fundação Oswaldo Cruz
> Rua Leopoldo Bulhões 1480 - 8A
> 21041-210  Rio de Janeiro - RJ
> Brazil
> E-mail: paulo.barata at ensp.fiocruz.br
> 
> ______________________________________________
> R-help at r-project.org mailing list
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> 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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