[R] How to modify a column of a matrix

[Marc Schwartz]

On Mon, 2007-03-12 at 18:55 +0100, Sergio Della Franca wrote:
> Dear R-helpers,
> 
> I'm trying to create a string-code to modify the contents of a column of a
> matrix.
> 
> For example, I have this dataset:
> 
>   YEAR   PRODUCTS
>   1992      3253
>   1993      4144
>   1994      3246
>   1996      4144
>   1997      4087
>   1998      3836
>   1999      4379
>   2000      4072
>   2001      4202
>   2002      4554
>   2003      4456
>   2004      4738
>   2005      4144
> 
> I want to convert/update the values of the column "PRODUCTS" under some
> condition (i.e. when the values of PRODUCTS is greather than 4000 replace
> the values of PRODUCTS whit 0 else replace with 1).
> 
> My question is the following:
> there is a function or a metodology that allow to makes this operation?
> 
> 
> Thank you in advance,
> Sergio

If the data is above is matrix (MAT) and not a data frame:

# See ?cbind and ?ifelse

MAT <- cbind(MAT,  NewCol = ifelse(MAT[, "PRODUCTS"] > 4000, 0, 1))

> MAT
   YEAR PRODUCTS NewCol
1  1992     3253      1
2  1993     4144      0
3  1994     3246      1
4  1996     4144      0
5  1997     4087      0
6  1998     3836      1
7  1999     4379      0
8  2000     4072      0
9  2001     4202      0
10 2002     4554      0
11 2003     4456      0
12 2004     4738      0
13 2005     4144      0


If it is a data frame:

DF$NewCol <- ifelse(DF$PRODUCTS > 4000, 0, 1)

> DF
   YEAR PRODUCTS NewCol
1  1992     3253      1
2  1993     4144      0
3  1994     3246      1
4  1996     4144      0
5  1997     4087      0
6  1998     3836      1
7  1999     4379      0
8  2000     4072      0
9  2001     4202      0
10 2002     4554      0
11 2003     4456      0
12 2004     4738      0
13 2005     4144      0


HTH,

Marc Schwartz