[R] Partial correlations and p-values

[dadrivr]

Awesome, that's what I was looking for.  I have two additional questions: (1)
What can I do if the variables are of different lengths? (2) How do I update
the formula if I want to control for more than one variable.

Let's take the following example:
x <- c(1,20,14,7,9)
y <- c(5,6,7,9,10,11)
z <- c(13,27,16,5,4,17,20)
a <- c(4,6,7,1)

xres <- residuals(lm(x ~ z))
yres <- residuals(lm(y ~ z))
cor(xres, yres)
ct <- cor.test(xres, yres)
ct$estimate
ct$p.value

How do I update the above formula to:
(1) take into account that the variables are of different lengths?  I get an
error when calculating the residuals.
(2) control for z and a (i.e., more than one variable)?

Thanks so much for your help.


Peter Ehlers wrote:
> 
> 
> dadrivr wrote:
>> I'm trying to write code to calculate partial correlations (along with
>> p-values).  I'm new to R, and I don't know how to do this.  I have
>> searched
>> and come across different functions, but I haven't been able to get any
>> of
>> them to work (for example, pcor and pcor.test from the ggm package).
>> 
>> In the following example, I am trying to compute the correlation between
>> x
>> and y, while controlling for z (partial correlation):
>> 
>> x <- c(1,20,14,7,9)
>> y <- c(5,6,7,9,10)
>> z <- c(13,27,16,5,4)
>> 
>> What function can I append to this to find this partial correlation? 
>> Many
>> thanks!
> 
> I'm not sure what you need, but does this give you what
> you want:
> 
> xres <- residuals(lm(x ~ z))
> yres <- residuals(lm(y ~ z))
> cor(xres, yres)
> # [1] 0.9778857
> 
> or
> 
> ct <- cor.test(xres, yres)
> ct$estimate  # 0.9978857
> ct$p.value   # 0.003934582
> 
>   -Peter Ehlers
> 
>> 
>>
> 
> ______________________________________________
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
> 
> 

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