使用R中的data.table生成新变量

我只是想使用现有变量y_corn和y_soybeans生成名为y_avg_corn、y_avg_soybeans的新变量

下面的代码就是我正在使用的代码

setDT(df)[ YEAR <= 2011, y_avg_corn := mean(y_corn), by = countyfips]

setDT(df)[ YEAR <= 2011, y_avg_soybeans := mean(y_soybeans), by = countyfips]

setDT（df）[您需要的年份
mean（获取）（粘贴0（“y”），裁剪列表[i]））
您需要
mean（获取（粘贴0（“y”），裁剪列表[i]）
crop_list <- list("corn", "soybeans")

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

setDT(df)[ YEAR <= 2011, paste0("y_avg_", crop_list[i]) := mean(paste0("y_", crop_list[i])), by = countyfips]

}