On Jul 10, 2013, at 12:17 PM, Harry Mamaysky wrote:
> As I understand it rownames(aa) returns a copy of an attribute of aa. So
> changing the value of this vector should make the change to the copy of the
> row.names attribute. I would then have to set the original row.names equal to
> this copy to effect the change.
>
> So my question is why "rownames(aa)[2:4] <-" changes the original attribute
> rather than its copy?
I'm not sure how you decide that was happening. Your first paragraph seemed
correct:
aa <- data.frame( a=1:10,b=101:110 )
str(aa)
attributes(aa)
dput(aa)
`rownames<-`
> trace(`rownames<-`)
> rownames(aa)[2:4] <- c('row2','row3','row4')
trace: `rownames<-`(`*tmp*`, value = c("1", "row2", "row3", "row4",
"5", "6", "7", "8", "9", "10"))
You can see that R first builds a full length vector with the second argumens
to `rownames<-` fully expanded before doing the assignment to the 'row.names'
attribute.
>
> And the follow on question is whether it's possible to have "f(x)[2:4] <-"
> operate in the same way for some user defined replacement function f.
Take a look at the code:
`row.names<-.data.frame`
--
David.
>
> Sent from my iPhone
>
> On Jul 10, 2013, at 3:05 PM, David Winsemius <[email protected]> wrote:
>
>
> On Jul 10, 2013, at 11:47 AM, Harry Mamaysky wrote:
>
>> I know how to define replacement functions in R (i.e. ‘foo<-‘ <-
>> function(x,value) x<-value, etc.), but how do you define replacement
>> functions that operate on subsets of arrays (i.e. how do you pass an index
>> into foo)?
>> For example, why does the following use of “rownames” work?
>
> `rownames` of a dataframe is a vector, so indexing with "[" and a single
> vector of indices is adequate. I cannot really tell what your conceptual
> "why"-difficulty might be. This is just assignment within a vector. That is
> not really a "replacement function operating on a subset of an array" since
> rownames are not values of the dataframe .... and it's not an "array".
> (Careful use of terms is needed here.)
>
>
>>
>>> aa <- data.frame( a=1:10,b=101:110 )
>>
>>> aa
>>
>> a b
>>
>> 1 1 101
>>
>> 2 2 102
>>
>> 3 3 103
>>
>> 4 4 104
>>
>> 5 5 105
>>
>> 6 6 106
>>
>> 7 7 107
>>
>> 8 8 108
>>
>> 9 9 109
>>
>> 10 10 110
>>
>>> rownames(aa)[2:4] <- c('row2','row3','row4')
>>
>>> aa
>>
>> a b
>>
>> 1 1 101
>>
>> row2 2 102
>>
>> row3 3 103
>>
>> row4 4 104
>>
>> 5 5 105
>>
>> 6 6 106
>>
>> 7 7 107
>>
>> 8 8 108
>>
>> 9 9 109
>>
>> 10 10 110
>>
>>
>>
>>
>> Thanks,
>>
>> Harry
>>
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> [email protected] 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.
>
> David Winsemius
> Alameda, CA, USA
>
David Winsemius
Alameda, CA, USA
______________________________________________
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