汇总在两列上

Question

我有一个数据集，其中包含来自商店不同分支的商品价格，看起来像这样：

Item,Chain,Branch1,Branch2,Branch3
Laptop,Sears,1000,1100,900
Laptop,JCP,1300,900,1200
Laptop,Macys,1500,1800,1700
TV,Sears,800,600,700
TV,JCP,400,600,700
TV,Macys,900,1000,1100

我想要的是：对于项和链的每个唯一组合，请计算三个分支的中间价格。

我尝试了类似的方法

aggregate(data[,3:5], list(data$Item, data$Chain), median)

但是没有用。关于如何解决此问题的任何想法？

Answer 1

您可以使用group_by()和summarise()：

library(dplyr)

df <- data_frame(Item = c("Laptop","Laptop","Laptop","TV","TV","TV"),
                 Chain = c("Sears","JCP","Macys","Sears","JCP","Macys"),
                 Branch1 = c(1000,1300,1500,800,400,900),
                 Branch2 = c(1100,900,1800,600,600,1000),
                 Branch3 = c(900,1200,1700,700,700,1100))

df %>%
  group_by(Item, Chain) %>%
  summarise(median = median(c(Branch1, Branch2, Branch3)))

Answer 2

问题是aggregate()汇总了每个列。

出于完整性考虑，以下是一些替代方法：

1。基数R按行apply()

dat$median <- apply(dat[, 3:5], 1L, median)
dat

     Item Chain Branch1 Branch2 Branch3 median
1: Laptop Sears    1000    1100     900   1000
2: Laptop   JCP    1300     900    1200   1200
3: Laptop Macys    1500    1800    1700   1700
4:     TV Sears     800     600     700    700
5:     TV   JCP     400     600     700    600
6:     TV Macys     900    1000    1100   1000

2。 data.table

library(data.table)
setDT(dat)[, .(median = median(c(Branch1, Branch2, Branch3))), by = .(Item, Chain)]

     Item Chain median
1: Laptop Sears   1000
2: Laptop   JCP   1200
3: Laptop Macys   1700
4:     TV Sears    700
5:     TV   JCP    600
6:     TV Macys   1000

3。 data.table重塑为长格式后

在合并之前，请遵循neilfws' suggestion从宽格式改成长格式：

library(data.table)
melt(setDT(dat), c("Item", "Chain"))[, .(median = median(value)), by = .(Item, Chain)]

     Item Chain median
1: Laptop Sears   1000
2: Laptop   JCP   1200
3: Laptop Macys   1700
4:     TV Sears    700
5:     TV   JCP    600
6:     TV Macys   1000

数据

由于data和df是R函数的名称，因此我将使用其他名称，以免难以调试名称冲突：

dat <- data.table::fread("
Item,Chain,Branch1,Branch2,Branch3
Laptop,Sears,1000,1100,900
Laptop,JCP,1300,900,1200
Laptop,Macys,1500,1800,1700
TV,Sears,800,600,700
TV,JCP,400,600,700
TV,Macys,900,1000,1100")