#Getting and Cleaning Data - Week 4
Playing with the formating
# upper, lower
toupper()
tolower()
# split
strsplit()
# replace
sub() #only the first occurence
gsub() #all occurences
# replace values
grep()
grepl()
Other useful string functions via stringr
library(stringr)
#count characters
nchar()
#substring
substr()
#concatenate
paste()
paste0()
#trim
str_trim()
General stuff about regex:
^xany line that starts with x$xany line that ends with x[Bb][Uu][Ss][Hh]any line that has bush in any cap size[0-9]any line that has at least 1 number[a-zA-Z]any line that has at least 1 char in any cap size[^xX]will reject any line that contains x or X9.11any line like 9x11, 9311, 9-11...x|X|ax OR X OR a[Gg]ood|[Bb]ad- Use
()to constrain on expressions :^(x|A)any line that starts by x or A - Use
?for optional constrains :[Gg]eorge ([Ww])? [Bb]ush - Use
\as the escape character :[Gg]eorge ([Ww]\.)? [Bb]ush +means at least one of the item :[0-9]+for at least one digit*means any number of the item including none :(.*)[0-9]+for any number of characters followed by at least one digit.*is greedy and won't stop at space, but you can change that with ```*?``{1,5}to specify a number of repetition allowed, here from 1 to 5
You can define areas with () and call them back with \1, \2...
Getdate()
date() # in character type
Sys.date() # in Date type
Formating date with expressions:
- %d : day of the month
- %a : abbreviated weekday
- %A : unabbreviated weekday
- %m : month (00-12)
- %b : abbreviated month
- %B : unabbreviated month
- %y : 2 digit year
- %Y : 4 digit year
format(Sys.date(),"%a %b %d")
as.Date("1jan1960", "%d%b%Y")
Great library to work with dates : Lubridate, works well with Time Savings and Time Zones
library(lubridate)
ymd("20140108")
mdy("08/04/2013")
dmy("03-04-2013)
ymd_hms("2011-08-03 10:15:03", tz="Pacific/Auckland")
?Sys.timezone
See slides