R help - Dec 2008 - Applying a function to a dataframe

Another Newbie Question sorry:

I am trying to apply a function a dataframe and could use some help:


Assuming, dim(df) = (10,2) say, I would like to apply a function that looks
at each row in turn and returns a list (dim =(10,1)) using the columns as
inputs to the function, but with no INDEX stuff that the by() function
refers to.

For a simple function x+y I know in Mathematica it would be this;

Table[df[[i,1]]+ df[[i,2]],{i,1,10}]

Of if the function was defined is would read;

Table[f[df[[i,1]], df[[i,2]]],{i,1,10}]

Thanks for help in advance

Glenn





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On Dec 16, 2008, at 6:00 PM, glenn roberts wrote:
> Another Newbie Question sorry:
>
> I am trying to apply a function a dataframe and could use some help:
>
>
> Assuming, dim(df) = (10,2) say, I would like to apply a function  
> that looks
> at each row in turn and returns a list (dim =(10,1)) using the  
> columns as
> inputs to the function, but with no INDEX stuff that the by() function
> refers to.
>
> For a simple function x+y I know in Mathematica it would be this;
>
> Table[df[[i,1]]+ df[[i,2]],{i,1,10}]
>
> Of if the function was defined is would read;
>
> Table[f[df[[i,1]], df[[i,2]]],{i,1,10}]
I don't know Mathematica, but if you just want the sum by rows

?apply

When the second argument is 1 the rows are taken singly as arguments  
to the third argument FUN:

 > DF <- data.frame(col1 = 1:10, col2 = 11:20)
 > apply(DF,1,sum)
  [1] 12 14 16 18 20 22 24 26 28 30


If you want minimums then the apply method  with FUN=min would still  
work:

 > apply(DF,1,min)
  [1]  1  2  3  4  5  6  7  8  9 10

>
>
> Thanks for help in advance
>
> Glenn
>
>
>
>
>
> 	[[alternative HTML version deleted]]
>
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