[R] Correlation Matrix

[David Winsemius]

On Apr 7, 2011, at 3:09 PM, Dmitry Berman wrote:

> Listers,
>
> I have a question regarding correlation matrices. It is fairly  
> straight
> forward to build a correlation matrix of an entire data frame. I  
> simply use
> the command cor(MyDataFrame). However, what I would like to do is  
> construct
> a smaller correlation matrix using just three of the variable out of  
> my data
> set.
>
> When I run this:
> cor(MyDataFrame$variable1, MyDataFrame$variable2,MyDataFrame 
> $variable3) I
> get an error.

But you choose not to offer it. Why is that?

>
> Is there a way to do this through a built in function or is this  
> something I
> have to construct manually?

Neither. You need to learn how R does argument matching:

 From help(cor)
"Usage:
cor(x, y = NULL, use = "everything", method = c("pearson", "kendall",  
"spearman"))"

So your 3 unnamed arguments were matched by position to `x`, `y` and  
`use`.
Try cor(x = myDataFrame[, c("variable1", "variable2", "variable3")]

-- 

David Winsemius, MD
West Hartford, CT