进行预测时找不到数据错误

Question

问题是：臂长为30 in。的个体的预计重复次数是多少？讨论线性逼近的适当性。

但是在尝试预测数据时遇到了问题。找不到BenchPress。

combine <- read.csv("C:/Users/Yuxi Liu/Desktop/nfl_combine2017.csv")
cols <- c("ArmLength", "BenchPress")
x <- combine$ArmLength 
y <- combine$BenchPress

combine_model = lm(ArmLength ~ BenchPress, data = combine)
confint(combine_model, conf.level=0.95)
summary((combine_model)$coefficients)

plot(ArmLength~ BenchPress, data = combine,
     xlab = "Arm Length",
     ylab = "Bench Press",
     main = "Arm Length vs Bench Press",
     pch = 10,
     cex = 1,
     col = "grey")
abline(lm(combine_model))

combine_model = lm(ArmLength ~ BenchPress, data = combine)
new.combine <- data.frame(x=c(30))
predict(combine_model, new.combine, se.fit = TRUE)

eval（predvars，data，env）中的错误：找不到对象'BenchPress'