R help - Oct 2007 - Strange names when creating a data.frame: Difference between <- and =

This is just a curiosity question.  Why do the two
different syntaxes for df1 and df2 give such different
results in the names(dfx)?

Thanks


df1 <- data.frame(nas = c("A",  "B" , "B"
,"C" ,"B",
"A", "D"),nums = c(3,    2,    1,   1,   2,    3,  7))

df2 <- data.frame(nas  <- c("A",  "B" , "B"
,"C" ,"B",
"A", "D"),nums  <- c(3,    2,    1,   1,   2,    3, 
7))

df1; df2
>df1
  nas nums
1   A    3
2   B    2
    .   .
>  df2
   nas....c..A....B....B....C....B....A....D..
nums....c.3..2..1..1..2..3..7.
1                                           A         
                    3
2                                           B         
                    
3
.                                           .

your two dataframe defintions are different.  In the case of df1, you
have 'names' the elements, and in the case of df2,you have done an
assignment to 'nam' and 'num' (look in the workspace and you
will see
the object.  Since you haven't names the elements in df2, is tries to
constuct a name from the expressions that is given (e.g., nums = c(3,
  2,    1,   1,   2,    3,  7)), so you get.

This is what happens:
> make.names("nums  <- c(3,    2,    1,   1,   2,    3, 7)")
[1] "nums.....c.3.....2.....1....1....2.....3..7."

It tries to make a name from the expression.

On 10/2/07, John Kane <jrkrideau at yahoo.ca>
wrote:
> This is just a curiosity question.  Why do the two
> different syntaxes for df1 and df2 give such different
> results in the names(dfx)?
>
> Thanks
>
>
> df1 <- data.frame(nas = c("A",  "B" , "B"
,"C" ,"B",
> "A", "D"),nums = c(3,    2,    1,   1,   2,    3,  7))
>
> df2 <- data.frame(nas  <- c("A",  "B" ,
"B" ,"C" ,"B",
> "A", "D"),nums  <- c(3,    2,    1,   1,   2,    3,
> 7))
>
> df1; df2
>
> >df1
>  nas nums
> 1   A    3
> 2   B    2
>    .   .
>
> >  df2
>
>   nas....c..A....B....B....C....B....A....D..
> nums....c.3..2..1..1..2..3..7.
> 1                                           A
>                    3
> 2                                           B
>
> 3
> .                                           .
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

John Kane-2 wrote:
> 
> This is just a curiosity question.  Why do the two
> different syntaxes for df1 and df2 give such different
> results in the names(dfx)?
> 
> Thanks
> 
> 
> df1 <- data.frame(nas = c("A",  "B" , "B"
,"C" ,"B",
> "A", "D"),nums = c(3,    2,    1,   1,   2,    3,  7))
> 
> df2 <- data.frame(nas  <- c("A",  "B" ,
"B" ,"C" ,"B",
> "A", "D"),nums  <- c(3,    2,    1,   1,   2,    3, 
> 7))
> 
> df1; df2
> 
>>df1
>   nas nums
> 1   A    3
> 2   B    2
>     .   .
> 
>>  df2
> 
>    nas....c..A....B....B....C....B....A....D..
> nums....c.3..2..1..1..2..3..7.
> 1                                           A         
>                     3
> 2                                           B         
>                     
> 3
> .                                           .
> 
You specify argument names in the first function call in the form
agrument.name=value
Argument names become column names in the data frame.
"<-" is the assignment operator, it returns the assigned value,  it
is not
the specification of a function argument. 

Second function call does not contain argument names, so, they are
constructed from expressions.
You should have the variables nas and nums in your workspace now.
ls() should show them.
If you type data.frame (without parentheses, "(" and ")") on
the R command
prompt it will print the body of this function. You can study it and
discover how it works.
-- 
View this message in context:
http://www.nabble.com/Strange-names-when-creating-a-data.frame%3A-Difference-between-%3C--and-%3D-tf4557141.html#a13006205
Sent from the R help mailing list archive at Nabble.com.

On Tue, 2 Oct 2007, John Kane wrote:
> This is just a curiosity question.  Why do the two
> different syntaxes for df1 and df2 give such different
> results in the names(dfx)?
Because only in the second case did you specify the names in the call.
When you do nas <- c("A" ...) the argument has no name but you
create an
object called 'nas' in the calling environment (the workspace, it looks 
like).

Perhaps you are confused by thinking '=' is an assignment operator in R,
but it is so only when it is not used in any other sense.
>
> Thanks
>
>
> df1 <- data.frame(nas = c("A",  "B" , "B"
,"C" ,"B",
> "A", "D"),nums = c(3,    2,    1,   1,   2,    3,  7))
>
> df2 <- data.frame(nas  <- c("A",  "B" ,
"B" ,"C" ,"B",
> "A", "D"),nums  <- c(3,    2,    1,   1,   2,    3,
> 7))
>
> df1; df2
>
>> df1
>  nas nums
> 1   A    3
> 2   B    2
>    .   .
>
>>  df2
>
>   nas....c..A....B....B....C....B....A....D..
> nums....c.3..2..1..1..2..3..7.
> 1                                           A
>                    3
> 2                                           B
>
> 3
> .                                           .
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

To everyone who answered

Many thanks for the explanations. I think I see what
is happening now