ref: R语言——日期时间处理
ref: as.Date: Date Conversion Functions to and from Character
ref: Date Formats in R
as.Date()it can change a normal string into a date format.
format()It can extract the specific date format from a date string.
Example:
> d = "2020-02-21"
> format(as.Date(d), format="%B, %Y")
[1] "February, 2020"
> format(as.Date(d), format="%d %B, %Y")
[1] "21 February, 2020"
> format(as.Date(d), format="%d %B, %Y, %A")
[1] "21 February, 2020, Friday"Date Formats
| Conversion specification | Description | Example |
| %a | Abbreviated weekday | Sun, Thu |
| %A | Full weekday | Sunday, Thursday |
| %b or %h | Abbreviated month | May, Jul |
| %B | Full month | May, July |
| %d | Day of the month 01-31 |
27, 07 |
| %j | Day of the year 001-366 |
148, 188 |
| %m | Month 01-12 |
05, 07 |
| %U | Week 01-53 with Sunday as first day of the week |
22, 27 |
| %w | Weekday 0-6 Sunday is 0 |
0, 4 |
| %W | Week 00-53 with Monday as first day of the week |
21, 27 |
| %x | Date, locale-specific | |
| %y | Year without century 00-99 |
84, 05 |
| %Y | Year with century on input: 00 to 68 prefixed by 20 69 to 99 prefixed by 19 |
1984, 2005 |
| %C | Century | 19, 20 |
| %D | Date formatted %m/%d/%y | 05/27/84, 07/07/05 |
| %u | Weekday 1-7 Monday is 1 |
7, 4 |
| %n | Newline on output or Arbitrary whitespace on input |
|
| %t | Tab on output or Arbitrary whitespace on input |