R studio：如何扩展时间序列并为缺失值填写 0？

Question

我有两张桌子：

一个是“visits”表：

+--------+---------+--------+
|  date  | user_id | visits |
+--------+---------+--------+
| 1/1/18 |    A    |    2   |
+--------+---------+--------+
| 1/2/18 |    A    |    4   |
+--------+---------+--------+
| 1/3/18 |    A    |   10   |
+--------+---------+--------+
| 1/4/18 |    A    |   34   |
+--------+---------+--------+
| 1/5/18 |    A    |   23   |
+--------+---------+--------+
| 1/1/18 |    B    |   15   |
+--------+---------+--------+
| 1/2/18 |    B    |   12   |
+--------+---------+--------+
| 1/1/18 |    C    |   10   |
+--------+---------+--------+
| 1/1/18 |    D    |    5   |
+--------+---------+--------+
| 1/2/18 |    D    |   12   |
+--------+---------+--------+
| 1/3/18 |    D    |   15   |
+--------+---------+--------+
| 1/4/18 |    D    |   25   |
+--------+---------+--------+
| 1/1/18 |    E    |   18   |
+--------+---------+--------+
| 1/1/18 |    G    |   21   |
+--------+---------+--------+
| 1/2/18 |    G    |   10   |
+--------+---------+--------+

另一个是“location”表：

+---------+----------+
| user_id | location |
+---------+----------+
|    A    |     1    |
+---------+----------+
|    B    |     1    |
+---------+----------+
|    C    |     1    |
+---------+----------+
|    D    |     2    |
+---------+----------+
|    E    |     3    |
+---------+----------+
|    F    |     3    |
+---------+----------+
|    G    |     3    |
+---------+----------+

注意：

• 1. 如果用户没有访问，他/她将不会出现在“访问”表中。他/她当天的访问量为 0。
• 1. “位置”表包含完整的用户群。

问题： 我想扩展“访问”表，使其看起来像这样：

+--------+---------+--------+
| date   | user_id | visits |
+--------+---------+--------+
| 1/1/18 |    A    | 2      |
+--------+---------+--------+
| 1/2/18 |    A    | 4      |
+--------+---------+--------+
| 1/3/18 |    A    | 10     |
+--------+---------+--------+
| 1/4/18 |    A    | 34     |
+--------+---------+--------+
| 1/5/18 |    A    | 23     |
+--------+---------+--------+
| 1/1/18 |    B    | 15     |
+--------+---------+--------+
| 1/2/18 |    B    | 12     |
+--------+---------+--------+
| 1/3/18 |    B    | 0      |
+--------+---------+--------+
| 1/4/18 |    B    | 0      |
+--------+---------+--------+
| 1/5/18 |    B    | 0      |
+--------+---------+--------+
| 1/1/18 |    C    | 10     |
+--------+---------+--------+
| 1/2/18 |    C    | 0      |
+--------+---------+--------+
| 1/3/18 |    C    | 0      |
+--------+---------+--------+
| 1/4/18 |    C    | 0      |
+--------+---------+--------+
| 1/5/18 |    C    | 0      |
+--------+---------+--------+
| 1/1/18 |    D    | 5      |
+--------+---------+--------+
| 1/2/18 |    D    | 12     |
+--------+---------+--------+
| 1/3/18 |    D    | 15     |
+--------+---------+--------+
| 1/4/18 |    D    | 25     |
+--------+---------+--------+
| 1/5/18 |    D    | 0      |
+--------+---------+--------+
| 1/1/18 |    E    | 18     |
+--------+---------+--------+
| 1/2/18 |    E    | 0      |
+--------+---------+--------+
| 1/3/18 |    E    | 0      |
+--------+---------+--------+
| 1/4/18 |    E    | 0      |
+--------+---------+--------+
| 1/5/18 |    E    | 0      |
+--------+---------+--------+
| 1/1/18 |    F    | 0      |
+--------+---------+--------+
| 1/2/18 |    F    | 0      |
+--------+---------+--------+
| 1/3/18 |    F    | 0      |
+--------+---------+--------+
| 1/4/18 |    F    | 0      |
+--------+---------+--------+
| 1/5/18 |    F    | 0      |
+--------+---------+--------+
| 1/1/18 |    G    | 21     |
+--------+---------+--------+
| 1/2/18 |    G    | 10     |
+--------+---------+--------+
| 1/3/18 |    G    | 0      |
+--------+---------+--------+
| 1/4/18 |    G    | 0      |
+--------+---------+--------+
| 1/5/18 |    G    | 0      |
+--------+---------+--------+

这种格式的表格更容易让我在一张表格中对整个人口进行进一步分析。

我想在 R 中对此进行编码，最好使用 tidyverse。 我无法理解如何实现这一目标。感谢对此的任何见解和帮助。非常感谢！

Answer 1

我们这里可能需要complete

library(dplyr)
library(tidyr)
visits %>% 
   complete(date, user_id = location$user_id, fill = list(visits = 0))