[R] Unexpected behavior when giving a value to a new variable based on the value of another variable

Angel Rodriguez angel.rodriguez at matiainstituto.net
Mon Sep 1 13:08:21 CEST 2014

Thank you John, Jim, Jeff and both Davids for your answers.

After trying different combinations of values for the variable samplem, it looks like if age is greater than 65, R applies the correct code 1 whatever the value of samplem, but if age is less than 65, it just copies the values of samplem to sample. I do not understand why it does so.

In any case, Jim's syntax work very well, although I do not understand why either.

Answering to Jim, I just wanted a variable that could identify individuals with some characteristics (not only age, as in this example that has been oversimplified).

Best regards,

Angel Rodriguez-Laso

-----Mensaje original-----
De: John McKown [mailto:john.archie.mckown at gmail.com]
Enviado el: vie 29/08/2014 14:46
Para: Angel Rodriguez
CC: r-help
Asunto: Re: [R] Unexpected behavior when giving a value to a new variable based on the value of another variable
On Fri, Aug 29, 2014 at 3:53 AM, Angel Rodriguez
<angel.rodriguez at matiainstituto.net> wrote:
> Dear subscribers,
> I've found that if there is a variable in the dataframe with a name very similar to a new variable, R does not give the correct values to this latter variable based on the values of a third value:
> Any clue for this behavior?
> Thank you very much.
> Angel Rodriguez-Laso
> Research project manager
> Matia Instituto Gerontologico

That is unusual, but appears to be documented in a section from


Character indices

Character indices can in some circumstances be partially matched (see
pmatch) to the names or dimnames of the object being subsetted (but
never for subassignment). Unlike S (Becker et al p. 358)), R never
uses partial matching when extracting by [, and partial matching is
not by default used by [[ (see argument exact).

Thus the default behaviour is to use partial matching only when
extracting from recursive objects (except environments) by $. Even in
that case, warnings can be switched on by
options(warnPartialMatchDollar = TRUE).

Neither empty ("") nor NA indices match any names, not even empty nor
missing names. If any object has no names or appropriate dimnames,
they are taken as all "" and so match nothing.

Note the commend about "partial matching" in the middle paragraph in
the quote above.

There is nothing more pleasant than traveling and meeting new people!
Genghis Khan

Maranatha! <><
John McKown

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