[R] Learning, "if" and "else"

[Paulo Brando]

Dear Rs,

I have tried to use conditional expressions to calculate biomass for
different life forms (trees, lianas, and palms).

Here is an example:

> lifeform

    dbh  form
1   30  tree
2   29  tree
3   28  tree
4   27  tree
5   26  tree
6   25  tree
7   24  tree
8   23  tree
9   22  tree
10  21  tree
11  20  tree
12  15 liana
13  14 liana
14  13 liana
15  12 liana
16  11 liana
17  10 liana
18   9 liana
19   8 liana
20   7 liana
21   6 liana
22   5 liana
23  30  palm
24  29  palm
25  28  palm
26  27  palm
27  26  palm
28  25  palm
29  24  palm
30  23  palm
31  22  palm
32  21  palm
33  20  palm

### I want to include biomass 

lifeform$biomass <- 

{
      if(lifeform$form=="tree")
       exp(-4.898+4.512*log(dbh)-0.319*(log(dbh))^2) 
       else{ 
        if (lifeform$form=="liana")
       10^(0.07 + 2.17 * log10 (dbh))
       else ("NA")
}
Warning message:
the condition has length > 1 and only the first element will be used in:
if (lifeform$form == "tree") exp(-4.898 + 4.512 * log(dbh) -


### But I always get the message warning message above. 



I looked for similar examples in R mail list archive, but they did not
help a lot.

I am quite new to 'R'. Any material that covers this theme?

Thank you very much!

Paulo

PS. Sorry about the last e-mail. I did not change the message title.
________________________________________
Paulo M. Brando
Instituto de Pesquisa Ambiental da Amazonia (IPAM)
Santarem, PA, Brasil.
Av. Rui Barbosa, 136.
Fone: + 55 93 522 55 38
www.ipam.org.br
E-mail: pmbrando at ipam.org.br