[R] adding a factor column based on levels of another factor

[Henrik Andersson]

First create a dataframe with the translation you want, i.e.

one column with the species and another with the number you want in the end.

Then merge these two dataframes using 'merge' and voila..

I would start with looking at ?merge

Cheers, Henrik Andersson

Karen Kotschy wrote:
> Hi R users
> 
> Does anyone out there have a better/quicker way of adding a factor column
> to a data frame based on levels of another factor?
> 
> I have a (large) data frame consisting of records for individual plants,
> each represented by a unique ID number. The species of each plant is
> indicated in the column "species", which is a factor column with many
> different levels (species). There are multiple records for each species,
> and there is no pattern to the order in which the species names appear in
> the data frame.
> 
> e.g.
>    uniqueID species   elev   ht   diam
> 1  1        sp2       3.5    1.3  55
> 2  2        sp2       4.2    0.5  15
> 3  3        sp3       3.2    1.0  13
> 4  4        sp65      2.2    2.0  14
> 5  5        sp43      5.4    5.7  20
> 6  6        sp2       2.5    4.1  32
> 7  7        sp12      1.1    0.9  5
> 8  8        sp3       3.4    3.6  2
> 
> I would like to add a factor column to this data frame, indicating to
> which group each individual belongs. All individuals of the same species
> will belong to the same group.
> 
> Is there a quick way of saying "for all instances of species1, give the
> value 5, for all instances of species2, give the value 4, etc" (where 5
> and 4 are levels of a factor)?
> 
> The only way I can think of doing it is to split the data frame by
> species, then add a column to each subset showing the group, then
> re-join all the subsets. This seems clumsy and prone to errors. Anyone
> know a better way?
> 
> I've looked at expand.grid and gl but they don't seem to do what I want.
> 
> Thanks!
> 
> Karen Kotschy
> Centre for Water in the Environment
> University of the Witwatersrand
> Johannesburg
> South Africa
> 
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-- 
---------------------------------------------
Henrik Andersson
Netherlands Institute of Ecology -
Centre for Estuarine and Marine Ecology
P.O. Box 140
4400 AC Yerseke
Phone: +31 113 577473
h.andersson at nioo.knaw.nl
http://www.nioo.knaw.nl/ppages/handersson