nottem df <- data.frame(f = nottem) str(df) f2c <- function(x) (x-32)*5/9 df <- data.frame(c =f2c(nottem)) str(df) df$ho <- 1:12 fit <- lm(df$c ~ df$ho) fit plot(1:240, df$c, type = "l") lines(predict(fit), col="red") fit <- lm(df$c ~ poly(df$ho, 2)) fit plot(1:240, df$c, type = "l") lines(predict(fit), col="red") decompose(df$c) plot(decompose(df$c))