[R] Hidden information in an object

Ista Zahn istazahn at gmail.com
Thu Feb 28 21:55:00 CET 2013

Hi Rasmus,

Things will be much less confusing if you don't use attach. I know
that sounds flippent, but I'm quite serious.


On Thu, Feb 28, 2013 at 7:50 AM, Rasmus Hedegaard
<hedegaard_84 at hotmail.com> wrote:
> Hello, The dataset "cats" contain information about the heart weight ("Hwt"), body weight ("Bwt") and gender ("Sex") of a group of 144 cats. I write the following piece of code: library(MASS)attach(cats)ratio <- Hwt/Bwtmale <- ratio[Sex == "M"]female <- ratio[Sex == "F"] My question is, when I look at the object "ratio", it is just a list of 144 numbers with no information about the gender of the cat that the ratio comes from, and yet the command "ratio[Sex == "M"]" is able to pick out those numbers of "ratio" for which the corresponding cat is male. Why is this? If I write the code like library(MASS)cats$ratio <- cats$Hwt/cats$Bwtmale <- cats$ratio[cats$Sex == "M"]... it also works, which I suppose is because there is a correspondence between the "Sex" variable and the "ratio" variable in the cats dataset. Regards,Rasmus Hedegaard.
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