statar

Matthieu Gomez

2016-06-24

Elapsed dates

The classes “monthly” and “quarterly” print as dates and are compatible with usual time extraction (ie month, year, etc). Yet, they are stored as integers representing the number of elapsed periods since 1970/01/0 (resp in week, months, quarters). This is particularly handy for simple algebra:

 # elapsed dates
 library(lubridate)
 date <- mdy(c("04/03/1992", "01/04/1992", "03/15/1992"))  
 datem <- as.monthly(date)
 # displays as a period
 datem
 #> [1] "1992m04" "1992m01" "1992m03"
 # behaves as an integer for numerical operations:
 datem + 1
 #> [1] "1992m05" "1992m02" "1992m04"
 # behaves as a date for period extractions:
 year(datem)
 #> [1] 1992 1992 1992

lag / lead

tlag/tlead a vector along a time variable (and NOT with respet to a number of row)

year <- c(1989, 1991, 1992)
value <- c(4.1, 4.5, 3.3)
tlag(value, 1, time = year)
library(lubridate)
date <- mdy(c("01/04/1992", "03/15/1992", "04/03/1992"))
datem <- as.monthly(date)
value <- c(4.1, 4.5, 3.3)
tlag(value, time = datem) 

In constrast to comparable functions in zoo and xts, these functions can be applied to any vector. This allows them to be used within a dplyr chain:

df <- data_frame(
    id    = c(1, 1, 1, 2, 2),
    year  = c(1989, 1991, 1992, 1991, 1992),
    value = c(4.1, 4.5, 3.3, 3.2, 5.2)
)
df %>% group_by(id) %>% mutate(value_l = tlag(value, time = year))

is.panel

is.panel checks whether a dataset is a panel i.e. the time variable is never missing and the combinations (id, time) are unique.

df <- data_frame(
    id1    = c(1, 1, 1, 2, 2),
    id2   = 1:5,
    year  = c(1991, 1993, NA, 1992, 1992),
    value = c(4.1, 4.5, 3.3, 3.2, 5.2)
)
df %>% group_by(id1) %>% is.panel(year)
df1 <- df %>% filter(!is.na(year))
df1 %>% is.panel(year)
df1 %>% group_by(id1) %>% is.panel(year)
df1 %>% group_by(id1, id2) %>% is.panel(year)

fill_gap

fill_gap transforms a unbalanced panel into a balanced panel. It corresponds to the stata command tsfill. Missing observations are added as rows with missing values.

df <- data_frame(
    id    = c(1, 1, 1, 2),
    datem  = as.monthly(mdy(c("04/03/1992", "01/04/1992", "03/15/1992", "05/11/1992"))),
    value = c(4.1, 4.5, 3.3, 3.2)
)
df %>% group_by(id) %>% fill_gap(datem)
df %>% group_by(id) %>% fill_gap(datem, full = TRUE)
df %>% group_by(id) %>% fill_gap(datem, roll = "nearest")