由两个变量求和 [英] Sum by two variables

问题描述

我有一个数据框:

       Date  area      sales
1     201204 shanghai    23
2     201204 beijing     25
3     201204 beijing     16
4     201205 shanghai    55
5     201205 beijing     17
6     201205 shanghai    16

我要输出的是一个表格如下:

What I want to output is a table as follows:

Date   shanghai  beijing 
201204  23        41
201205  71        17

我将如何在 R 中执行此操作?

How would I do this in R?

推荐答案

在基础 R(对于 sum)中有 xtabs:

In base R (for sum) there's xtabs:

> xtabs(sales ~ Date + area, mydf)
        area
Date     beijing shanghai
  201204      41       23
  201205      17       71

要将其作为 data.frame 获取，请将其包装在 as.data.frame.matrix 中.

To get it as a data.frame, wrap it in as.data.frame.matrix.

要使用最近流行的方法更新它，您还可以使用dplyr"(用于聚合)和tidyr"(用于重塑)的组合，如下所示:

To update this with the approach that is making the rounds these days, you can also use a combination of "dplyr" (for aggregation) and "tidyr" (for reshaping), like this:

library(tidyr)
library(dplyr)
mydf %>% 
  group_by(Date, area) %>% 
  summarise(sales = sum(sales)) %>% 
  spread(area, sales)
# Source: local data frame [2 x 3]
# 
#     Date beijing shanghai
# 1 201204      41       23
# 2 201205      17       71

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