There are many techniques Callum and yours is an interesting twist I had not
considered.
Yes, you can specify what integer a factor uses to represent things but not
what I meant. Of course your trick does not work for some other forms of data
like real numbers in double format. There is a cost to converting a column to a
factor that is recouped best if it speeds things up multiple times.
The point I was making was that when you will be using group_by, especially if
done many times, it might speed things up if the column is already a normal
factor, perhaps just indexed from 1 onward. My guess is that underneath the
covers, some programs implicitly do such a factor conversion if needed. An
example might be aspects of the ggplot program where you may get a mysterious
order of presentation in the graph unless you create a factor with the order
you wish to have used and avoid it making one invisibly.
From: CALUM POLWART <[email protected]>
Sent: Saturday, November 4, 2023 7:14 PM
To: [email protected]
Cc: Jorgen Harmse <[email protected]>; [email protected]; [email protected]
Subject: Re: [R] I need to create new variables based on two numeric variables
and one dichotomize conditional category variables.
I might have factored the gender.
I'm not sure it would in any way be quicker. But might be to some extent
easier to develop variations of. And is sort of what factors should be doing...
# make dummy data
gender <- c("Male", "Female", "Male", "Female")
WC <- c(70,60,75,65)
TG <- c(0.9, 1.1, 1.2, 1.0)
myDf <- data.frame( gender, WC, TG )
# label a factor
myDf$GF <- factor(myDf$gender, labels= c("Male"=65, "Female"=58))
# do the maths
myDf$LAP <- (myDf$WC - as.numeric(myDf$GF))* myDf$TG
#show results
head(myDf)
gender WC TG GF LAP
1 Male 70 0.9 58 61.2
2 Female 60 1.1 65 64.9
3 Male 75 1.2 58 87.6
4 Female 65 1.0 65 64.0
(Reality: I'd have probably used case_when in tidy to create a new numeric
column)
The equation to
calculate LAP is different for male and females. I am giving both equations
below.
LAP for male = (WC-65)*TG
LAP for female = (WC-58)*TG
My question is 'how can I calculate the LAP and create a single new column?
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