Getting and cleaning data——Week4

Editing text variables

• Fixing character vectors
  • tolower()
  • toupper()
  • strsplit()
    
  • sub()
    
  • gsub() globle version of sub
• Finding values
  • grep()
  • grepl() if exist, function will return TRUE, otherwise
    return FALSE
    
• 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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