[R] How to compare X1 = X2 = ... = Xn?

[Liaw, Andy]

Here's an alternative:

> x <- data.frame(X1 = c(1, 1, 2, 4),
+                  X2 = c(4, 1, 2, 5),
+                  X3 = c(2, 1, 2, 2))
> check <- paste(names(x), collapse=" == ")
> with(x, eval(parse(text=check)))
[1] FALSE  TRUE FALSE FALSE

Cheers,
Andy


> From: Sundar Dorai-Raj
> 
> F Duan wrote:
> 
> > Dear All,
> > 
> > I have a data frame with n columns: X1, X2, ., Xn. Now I 
> want to create a
> > new column: if X1 = X2 = . = Xn, the value is 1; Otherwise, 
> the value is 0.
> > 
> > How to do that in a quick way instead of doing (n choose 2) 
> comparisons? 
> > 
> > Thank you,
> > 
> > Frank
> 
> How about something like?
> 
> x <- data.frame(X1 = c(1, 1, 2, 4),
>                  X2 = c(4, 1, 2, 5),
>                  X3 = c(2, 1, 2, 2))
> nuniq <- function(x) length(unique(x))
> as.numeric(apply(as.matrix(x), 1, nuniq) == 1)
> 
> --sundar
> 
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