[R] Classifying values by interval

[Dimitris Rizopoulos]

Probably you're looking for function findInterval().


I hope it helps.

Best,
Dimitris



On 8/31/2011 10:00 AM, Ted Harding wrote:
> Greetings All!
> As is often the case on this list, the answer may well
> be under my nose but I can't see it!
>
> I am looking for a "smart" way to do the following.
>
> Say I have a vector of values, X. I set up bins" for X,
> say with breaks at B = c(b1,b2,...,b11) covering the
> range of X, i.e. bins numbered 1:10. The value x is in
> bin i if B[i]<  x<= B[i+1]
>
> What I seek is a vector, of the same length as X, which
> for each x in X gives the number of the bin that x is in.
>
> Clearly this can be done in an "unsmart" way by looping
> through all of X along with something like
>
>    which( (B[1:10]<  X[j])&  (X[j]<= B[2:11]) )
>
> However, I feel that this naturally occurring task must
> have received a smarter solution! The hist() function
> already does this implicitly, since it has to decide
> which bin a value in X should be counted in. But it
> apparently then discards this information, since there
> is nothing relevant in the return values from hist().
>
> So is there a "smart" function somewhere for this?
>
> The motivation here is that I have multivariate data,
> (X,Y,Z,...) and I wish to study how it behaves in each
> different bin for X. So the "bin index", ixB aY, derived
> for X can be applied to select corresponding subsets of
> the other variables. Rather than doing it the clumsy
> way each time, e.g. according to
>
>    Y[(B[i]<  X)&  (X<= B[j+1])]
>
> I would like to have the bin index permanently available
> -- for example it allows easy logical combinations of
> bins, such as Y[(ixB==j1) | (ixB==j2)], or Y[(ixB %in% ixB0)].
>
> With thanks,
> Ted.
>
> --------------------------------------------------------------------
> E-Mail: (Ted Harding)<ted.harding at wlandres.net>
> Fax-to-email: +44 (0)870 094 0861
> Date: 31-Aug-11                                       Time: 09:00:27
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-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
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