如何从代码中查找值并基于它创建一些新列

Question

我想从数据库中查找值并在文件中创建一些新列实际上我有一个这样的文件

promo code item stok
sale1  100   a   200
sale2  101   b   300
sale3  102   c   100
sale4  103   d    50

数据库看起来像这样

code item1 code_item1 amount_item1 item2 code_item2 amount_item2 
100   a1     1001          2        a2     1002          1
102   a2     1002          1        a3     1003          1

然后我想在我的第一个文件中添加从数据库中提取的几列

promo code item stok item1 code_item1 amount_item1 item2 code_item2 amount_item2
sale1  100   a   200   a1     1001          400        a2     1002          200
sale2  101   b   300
sale3  102   c   100   a2     1002          100        a3     1003          100
sale4  103   d    50

我该怎么做？

Answer 1

您可以使用 left_join() 来自 dplyr:

library(dplyr)

my_df <- data.frame(promo = c("sale1", "sale2", "sale3", "sale4"), code = c(100, 101, 102, 103), item = c("a", "b", "c", "d"), stok = c(200, 300, 100, 50))
db_df <- data.frame(code = c(100, 102), item1 = c("a1", "a2"), code_item1 = c(1001, 1002), amount_item1 = c(2,1), item2 = c("a2", "a3"), code_item2 = c(1002, 1003), amount_item2 = c(1,1))

result_df <- left_join(my_df, db_df, by = c("code" = "code"))
result_df

  promo code item stok item1 code_item1 amount_item1 item2 code_item2 amount_item2
1 sale1  100    a  200    a1       1001            2    a2       1002            1
2 sale2  101    b  300  <NA>         NA           NA  <NA>         NA           NA
3 sale3  102    c  100    a2       1002            1    a3       1003            1
4 sale4  103    d   50  <NA>         NA           NA  <NA>         NA           NA
>

编辑：与您的评论相关，您也可以在 left_join 之后进行乘法运算，之前不需要进行：

result_df$amount_item1 <- result_df$amount_item1 * result_df$stok
result_df$amount_item2 <- result_df$amount_item2 * result_df$stok

Answer 2

是的，dplyr 是不错的选择，但是我在这种情况下总是使用 merge()。

my_df <- data.frame(promo = c("sale1", "sale2", "sale3", "sale4"), code = c(100, 101, 102, 103), item = c("a", "b", "c", "d"), stok = c(200, 300, 100, 50))
db_df <- data.frame(code = c(100, 102), item1 = c("a1", "a2"), code_item1 = c(1001, 1002), amount_item1 = c(2,1), item2 = c("a2", "a3"), code_item2 = c(1002, 1003), amount_item2 = c(1,1))

result <- merge(x=my_df, y=db_df, by='code', all.x = TRUE)

> result
  code promo item stok item1 code_item1 amount_item1 item2 code_item2 amount_item2
1  100 sale1    a  200    a1       1001            2    a2       1002            1
2  101 sale2    b  300  <NA>         NA           NA  <NA>         NA           NA
3  102 sale3    c  100    a2       1002            1    a3       1003            1
4  103 sale4    d   50  <NA>         NA           NA  <NA>         NA           NA

如何从代码中查找值并基于它创建一些新列

How to lookup values from code and make some new columns based on it

lookup

r

match