The variables have the same length, but with different numbers of missing values (NA). As a result, the residuals calculations (xres & yres) have different lengths, and I cannot compute the correlation between the two (error of incompatible dimensions - see example below). Is there a way, when calculating residuals, to leave the NAs in the residual calculation and output? Thanks!
x <- c(1,20,14,NA,9) y <- c(5,6,7,9,10) z <- c(13,NA,16,14,NA) xres <- residuals(lm(x ~ z)) yres <- residuals(lm(y ~ z)) cor(xres, yres) ct <- cor.test(xres, yres) ct$estimate ct$p.value Ista Zahn wrote: > > 1) Think about what you did wrong. It doesn't make sense to do > correlation/regression with variables of different lengths. You can > have missing values in one or more variables, if that's what you mean. > Just code them NA. > > 2) Just add in the predictors, e.g. > residuals(lm(y ~ z1 + z2)) > > -Ista > > On Wed, Nov 11, 2009 at 10:34 PM, dadrivr <dadr...@gmail.com> wrote: >> >> 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 >>> >>>> >>>> >>> >>> ______________________________________________ >>> R-help@r-project.org mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-help >>> PLEASE do read the posting guide >>> http://www.R-project.org/posting-guide.html >>> and provide commented, minimal, self-contained, reproducible code. >>> >>> >> >> -- >> View this message in context: >> http://old.nabble.com/Partial-correlations-and-p-values-tp26308463p26312873.html >> Sent from the R help mailing list archive at Nabble.com. >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > > > -- > Ista Zahn > Graduate student > University of Rochester > Department of Clinical and Social Psychology > http://yourpsyche.org > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > > -- View this message in context: http://old.nabble.com/Partial-correlations-and-p-values-tp26308463p26318276.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
