[R] subtract 2 columns in a data.frame

[Petr Pikal]

   Hi

   On 4 Sep 2003 at 14:35, Ulrich Leopold wrote:

   > > E.g.,

   > >

   > > mydata$difference <- mydata$x - mydata$y

   > >

   >

   > That's what I thought, but I get the following message:

   >

   >  > propLSK.STONE.Pox0t30$Pox0t30STONE-propLSK.STONE.Pox0t30$Pox0t30

   > numeric(0)

   Beware of case sensitivity

   propLSK.STONE.Pox0t30$Pox0t30stone-propLSK.STONE.Pox0t30$Pox0t30

   shall work as expected

   A little bit less complicated names of data frames and variables could
   be more readable and more error prone.

   Cheers

   Petr

   >

   > Does it mean the resulting vector is empty? If yes, what could be
   the

   > reason for it? Both columns are available:

   >

   >       UGreen    Pox0t30 Pox0t30Stone

   > 1         0  37.150000    16.461500

   > 2         0   6.833330     7.464404

   > 3         0   9.750000    15.616870

   > 4         0  15.050000    19.146500

   > 5         0  13.266700    10.515750

   > 6         0  34.300000    27.304840

   > 7         0  45.800000    27.217171

   > 8        NA  23.200000    16.844601

   > 9         0  13.600000    28.051821

   > 10        0  16.750000     6.021914

   > 11        0  16.433300     3.832123

   > 12        0  17.333300     3.905555

   >

   >

   > What am I missing?

   >

   > Ulrich

   >

   >

   > --

   > __________________________________________________

   >

   > Ulrich Leopold MSc.

   >

   > Department of Physical Geography

   > Institute for Biodiversity and Ecosystem Dynamics

   > Faculty of Science

   > University of Amsterdam

   > Nieuwe Achtergracht 166

   > NL-1018WV Amsterdam

   >

   > Phone:         +31 20 525 7456 (7451 Secretary)

   > Fax:  +31 20 525 7431

   > Mobile:        +31 64 220 3028

   > Email:          uleopold at science.uva.nl

   >
   URL:           www.science.uva.nl/ibed/research/Research_Fields/fg/sta
   fffg/index

   > .html

   >

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   Petr Pikal

   petr.pikal at precheza.cz