CODEWITHSUNDEEP
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Olivia
Olivia

Reputation: 11

Creating variable names from varying lists

I am trying to create variable name from lists in R, but am struggling!

What I would ultimately like to do is to use previously created lists to create a formula for a multiple linear regression, whereby each value within the list will identify one of the explanatory variables of the regression formula.

I am starting with x lists of variable lengths (GoodModels_LMi, where i goes from 1 to x) and use each list to create a separate formula.

for (i in 1:x){
    lm(formula created from appropriate list)
    i<-i+1
    }

The lists correspond to variable numbers to be chosen from a data matrix (AllData). So for example if:

GoodModels_LM1<-c(2,4,8)

I would like my regression formula to be:

AllData[,1]~AllData[,2]+AllData[,4]+AllData[,8]

I have been trying to use as.formula() and paste() to achieve this, however, I am not sure how to create the second part of my formula.

as.formula(paste("AllData[,",i,"]~",paste(?????????)))

I know that this below is not right, but is as close as I have come: 

paste("AllData[,",paste("GoodModels_LM",i,sep=""),"]",collapse="+")

I have also looked into assign(), but have not succeeded as the value argument was the same as the x argument.

Thanks very much for any help with this!

Olivia

Upvotes: 1

Views: 280

Answers (1)

Andrie
Andrie

Reputation: 179438

Your formula should contain the column names, not the actual data. Here is a small demo using iris.

Imagine you want to run a regression using columns 2, 4, and 5 from iris. First, construct a formula using paste():

vars <- c(2, 4, 5)
frm <- paste("Sepal.Length ~ ", paste(names(iris)[vars], collapse=" + "))
frm

"Sepal.Length ~  Sepal.Width + Petal.Width + Species"

So, the object frm is a string containing a formula that you can pass to lm():

lm(frm, iris)
Call:
lm(formula = frm, data = iris)

Coefficients:
      (Intercept)        Sepal.Width        Petal.Width  
           2.5211             0.6982             0.3716  
Speciesversicolor   Speciesvirginica  
           0.9881             1.2376

Upvotes: 2

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