[R] How to substract a valur from dataframe with condition

[David Winsemius]

On Mar 21, 2011, at 5:39 PM, joe82 wrote:

> Hello All,
>
> I need help with my dataframe, it is big but here I am using a small  
> table
> as an example.
>
> My dataframe df looks like:
>        X1      X2    X3
> 1   2011-02  0.00 96.00
> 2   2011-02  0.00  2.11
> 3   2011-02  2.00  3.08
> 4   2011-02  0.06  2.79
> 5   2011-02  0.00 96.00
> 6   2011-02  0.00 97.00
> 7   2011-02  0.08  2.23
>
> I want values in columns X2 and X3 to be checked if they are greater  
> than
> 50, if yes, then subtract from '100'
>
> df should look like:
>
>       X1      X2    X3
> 1   2011-02  0.00 4.00
> 2   2011-02  0.00  2.11
> 3   2011-02  2.00  3.08
> 4   2011-02  0.06  2.79
> 5   2011-02  0.00 4.00
> 6   2011-02  0.00 3.00
> 7   2011-02  0.08  2.23


df[ , 2:3] <- apply(df[ , 2:3], 2,
                  function(x) ifelse(x >50, 100-x, x) )

OR:

df[ , 2:3] <- sapply(df[ , 2:3],
                  function(x) ifelse(x >50, 100-x, x) )

(or lapply would work as well)

OR;

df$X2[df$X2 >50] <- 100 - df$X2[df$X2 >50]
df$X1[df$X1 >50] <- 100 - df$X1[df$X1 >50]

-- 
David Winsemius, MD
Heritage Laboratories
West Hartford, CT