[R-sig-Finance] How to get values from dataframe's column conditional on other column

[Dirk Eddelbuettel]

On Tue, Jun 13, 2006 at 12:35:36PM +0100, Yuri Volchik wrote:
> Hi to all members of this list,
> 
> I'm quite a novice to R and was wondering if there is a more elegant
> way to solve a following problem:
> Suppose we have a dataframe
>   X     Y
> .12   TRUE
> -.24  TRUE
> ..     ...
> .34   FALSE
> 
> i.e. two (or more columns) with data and we want to get vector of X
> values conditional on Y values (say only X's when Y=TRUE).
> Of course it is possible to do it by looping through the whole
> dataframe, i was wondering if there is a a more elegant solution to
> this in R?

You would do yourself a huge favour if you read the 'An Introduction to R'
manual distributed with R, or, for that matter, any of the other contributed  
introductory manuals on the R/CRAN site.

The answer, by the way, is 

    DF[ DF[,"Y"]==TRUE, "X" ]

ie you create a boolean condution for the rows (and == 'TRUE' could be
omitted if Y is boolean), and then select "X".  There are still issues that
may confuse you about data.frames collapsing to a single vector, please go
and read the manual. Really.

Dirk

-- 
Hell, there are no rules here - we're trying to accomplish something. 
                                                  -- Thomas A. Edison