[R] merge function

[carol white]

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
>
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-- 
Michael
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