[R] Get the difference between two matrices with different length

[Philippe Grosjean]

Hello,

The answer is in one page of the R Wiki (just created to address such a 
question, by the way): 
http://wiki.r-project.org/rwiki/doku.php?id=tips:data-manip:calc_on_two_tables

..............................................<°}))><........
  ) ) ) ) )
( ( ( ( (    Prof. Philippe Grosjean
  ) ) ) ) )
( ( ( ( (    Numerical Ecology of Aquatic Systems
  ) ) ) ) )   Mons-Hainaut University, Belgium
( ( ( ( (
..............................................................

Felix Wave wrote:
> Hello,
> I have got two matrices with different length. The matrices have 3
> columuns. The first two are coordinates. The third is a measurement.
> 
> Now I want to get a subtraction between every single value of the 
> third column (between matrix1 and matrix2), but only if the two 
> first coordinates in matrix1 and matrix2 are the same.
> 
> I tried "FUN=?" in aggregate and ave, but I don't know the command
> for such a subtraction?
> 
> 
> Thank's a lot.
> Felix
> 
> 
> ---------------
> 
> The matrixes (examlple):
> 
> 1 0.1 0.0042
> 1 0.2 0.00423
> 1 0.4 0.00467
> 1 0.5 0.00518
> 1 0.6 0.0061
> 
> 
> 1 0.1 0.0043
> 1 0.2 0.00442
> 1 0.3 0.00433
> 1 0.4 0.0045
> 1 0.5 0.00524
> 1 0.7 0.006
> 
> 
> 
> My aim:
> -------
> 1 0.1 -0.0001
> 1 0.2 -0.00019
> 1 0.4 0.00017
> 1 0.5 -0.00006
> 
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