r如何将一个数据框中的选择变量应用到另一个数据框中的行公式中

Question

我有两个不同维度的数据框架，一个包含观察值，另一个包含与观察值相关的常数，用于算术运算。我想做的是从df2中选择适当的常数，用于df1中的行方向观测，以产生df3。

我附上了示例数据和一个简单的等式：

# df1 with annual observation data from different commodities

df1 <- data.frame(Region = c("Europe", "Asia", "N.Amer", "Africa"), 
                  Item = c("Wheat", "Barley", "Oats", "Rice"), 
                  Year = c(1961, 1961, 1961, 1961), 
                  Production = c(2000, 1000, 1500, 500), 
                  Imports = c(1000, 200, 3000, 100), 
                  Stock.Var = c(-100, 300, 50, 0), 
                  Exports = c(250, 150, 100, 200))

#df2 with constants for losses by commodity in different regions

df2 <- data.frame(Area = c("Asia", "N.Amer", "Europe", "Africa"),
                  Item = c("Wheat", "Oats", "Rice", "Barley"), 
                  LF1 = c(0.02, 0.1, 0.15, 0.05))

# df3 would contain the outputs from calculating losses from df1 by df2 by  row
# Equation: L1 = (Production + Imports + Stock.Var - Exports) * LF1

等式中LF1的值是根据项目从df2中获取的

df1的全尺寸是几十万行乘16列；df2约为150行乘20列。

Answer 1

这可以通过dplyr的＜code＞inner_join

library(dplyr)
df1 %>% inner_join(df2, by = c(Region = "Area", "Item")) %>%
    mutate(L1 = (Production + Imports + Stock.Var - Exports) * LF1)

如果你宁愿坚持使用以R为基数，你可以使用合并：

m <- merge(df1, df2, by.x = c("Region", "Item"), by.y = c("Area", "Item"))
m$L1 <- (m$Production + m$Imports + m$Stock.Var - m$Exports) * m$LF1