Create variables in loop in R

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R

I am trying to calculate a regression variable based on a range of variables in my data set. I would like the regression variable (ei: Threshold 1) to be calculated using a different variable set in each iteration of running the regression.

Data (df)is composed of variables: Yield, Prec, Price, 0C, 1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C

Regression:

reg <- lm(log(Yield)~Threshold1+Threshold2+log(Price)+prec+I(prec^2),data=df)
for EACH iteration of the Regression, I vary the components of calculating thresholds in the following manner:

Threshold example:

a <- df$0C
b <- df$1C

Threshold1 <- (a-b)

Threshold2 <- (b)
Where "b" would be changing in each loop, ranging from 1C to 9C.

Each individual threshold set (1 and 2) should be used to run a regression, and save the SSR for comparison with the subsequent regression utilizing thresholds based on a new "b" value (ranging from 1C TO 9C)

Current approach is centered around the following code:

df <- read.csv("Data.csv",header=TRUE)

names(df)
0C-9Cvarlist <- names(df)[9:19]
ssr.vec <- matrix(,21,1)

for(i in 1:length(varlist)){

a <- df$0C
b <- df$[i]

Threshold1 <- (a-b)

Threshold2 <- (b)

reg <- lm(log(Yield)~Threshold1+Threshold2+log(Price)+prec+I(prec^2),data=df)

r2 <- summary(reg)$r.squared

ssr.vec[i,] <- c(varlist,r2)
}

colnames(ssr.vec) <- c("varlist","r2")
Clearly the code above is not performing the task I am trying to achieve.

Any assistance in being pointed in the right direction would be extremely helpful. Thank you.