R Language Learning notes: Date processing

1. Take out the current date

Sys.date ()

[1] "2014-10-29"

Date () #注意: This method returns a string type

[1] "Wed Oct 29 20:36:07 2014"

2, in R the date is actually double type, is the number of days since January 1, 1970

typeof (Sys.date ())

[1] "double"

3. Convert to date

With AS. Date () can convert a string to a date value, and the default format is YYYY-MM-DD.

As. Date ("2007-02-01") #得到 "2007-02-01", which is displayed as a string, but is actually stored with a double

As.double (AS. Date ("1970-01-01")) #结果为0, is the number of days since January 1, 1970.

You can convert a custom date string to a date type

As. Date ("February 1, 2007", "%y year%m month%d Day")

[1] "2007-02-01"

Format	Significance
%Y	Year, expressed as four digits, 2007
%m	month, expressed in numbers, from 01 to 12
%d	Number of days in the month, from 01 to 31
%b	month, abbreviation, FEB
%B	month, full month name, English, February
%y	Year, expressed as two digits, 07

4. Output the date value as a string

Today <-Sys.date ()

Format (today, "%y year%m month%d Day")

[1] "October 29, 2014"

5. Calculation Date Difference

Because the date inside is the number of days stored in double, it can be subtracted.

Today <-Sys.date ()

GTD <-as. Date ("2011-07-01") #我是从2011年7月开始实践GTD的

Today-gtd

Time difference of 1216 days

Originally I have been practicing GTD for 1216 days.

Use the Difftime () function to calculate the number of seconds, minutes, hours, days, weeks, and months

Difftime (Today, GTD, units= "weeks") #还可以是 "secs", "mins", "hours", "Days"

Time difference of 173.7143 weeks

Continue to solve one of my practical problems with the R language: Count the data in the Fitbit pedometer and draw

# Read the Fitbit stats in CSV format

Fitbit <-read.csv ("Fitbit.csv")

# Date to convert

Fitbit$date <-as. Date (Fitbit$date, "%y year%m month%d Day")

# drawing, drawing only lines

Plot (Fitbit$date, Fitbit$step, type= "L")

# only statistics on the movement of the August

Fitbit8 <-fitbit[months (fitbit$date) = = "August",]
Plot (Fitbit8$date, Fitbit8$step, type= "L")

R language Learning Note: Date processing