[R] merge function

[Bert Gunter]

You do not appear to understand what merge() does. Go through the worked
examples in ?merge so that you do.

FWIW, I would agree that the Help file is cryptic and difficult to
understand. Perhaps going through a tutorial on database "join" operations
might help.

Cheers,
Bert

Bert Gunter

"Data is not information. Information is not knowledge. And knowledge is
certainly not wisdom."
   -- Clifford Stoll

On Mon, Jun 1, 2015 at 7:47 AM, carol white via R-help <r-help at r-project.org
> wrote:

> I understood that by would take the intersection of names(x) and names(y),
> names(x) being the column names of x and names(y), column names of y.
> if x has 5 col and the col names of x are col1, col2... col5 and y has 3
> col and their names are col1, col2, col3, I thought that the merged data
> set will have 3 col, namely col1, col2, col3 but all 5 col, i.e. col1,
> col2... col5 are taken if nothing is specified for the by arg.
> Cheers,
>
>
>
>      On Monday, June 1, 2015 4:32 PM, Michael Dewey <
> lists at dewey.myzen.co.uk> wrote:
>
>
>
>
> On 01/06/2015 14:46, carol white via R-help wrote:
> > Hi,By default the merge function should take the intersection of column
> names
>
>   (if this is understood from by = intersect(names(x), names(y)),
>
> Dear Carol
> The by parameter specifies which columns are used to merge by. Did you
> understand it to be which columns are retained in the result?
>
> Just a hunch, and if not then you need to give us a toy example.
>
>
>
>   but it takes all columns. How to specify the intersection of column
> names?
> >  Thanks
> > Carol
> >
> >     [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > 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.
> >
>
> --
> Michael
> http://www.dewey.myzen.co.uk/home.html
>
>
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.

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