[R] two easy questions...

[Stefano]

Hi all.

1) If I have a dataframe with variable names as follow: PC1 PC2 ... PCn and I want to pass only some of them to a function, e.g.
glm(resp~from PC1 to PC10, PC15, etc.,...)

is there a faster way than simply writing each variable name in the formula?

2) Again, I have a dataframe, say ali.df, with tha following variables: ali1, ali2, ...ali78
I want to sum, for example, ali1+al2+ali7+f rom ali10 to ali20 etc., then from ali4 to ali8, etc. and then put everything in a new dataframe

I'd do somthing like:
 
new.df <- cbind(apply(ali.df[c(1:2,7,10:20)],1,sum), apply(ali.df[4:8],1,sum))   and so on.
Is it the right and only way?


Thanks in advance (and forgive my orrible english...)

Stefano

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