Editing text variables
- Fixing character vectors
tolower()toupper()-
strsplit()
-
sub()
-
gsub()globle version of sub
- Finding values
grep()-
grepl()if exist, function will returnTRUE, otherwise
returnFALSE
- More useful string functions:
stringr- substr()
- paste()
- paste0
- str_trim()
Regular expressions
Metacharacters
-
^:Some metacharacters represent the start of a line -
$: represents the end of a line -
.: is used to refer to any (one) character -
|: OR -
():Subexpressions are often contained in parentheses to constrain the alternatives -
?:The question mark indicates that the indicated expression is optional -
*: means any number, characters -
+:means "at least one of the item -
{}:referred to as interval quantifiers; the let us specify the minimum and maximum number of matches of an expression
Character Classes with [] -
[]:list a set of characters we will accept at a given point in the match
Working with dates
-
date()得到的日期为字符串 -
Sys.Date()获取日期格式的日期 -
format()格式化日期： as.Date()-
julian()从1970-01-01起到日期为止的天数
lubridate
mdy()dmy()ymd_hms()wdays()
Data resources
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