CODEWITHSUNDEEP
rdatetime
Asteroid098
Asteroid098

Reputation: 2825

Create column based on datecolumn values in R

I wrote a function that creates column based on a datetime column using parameters starting and ending dates, but I can't get it to work.

df is a data frame object.

create_gv <- function(df, s_ymd, e_ymd, char) {
    df<-get(df)
    for (i in (1:nrow(df))) {
        ymd <- format(df[i,1],"%y%m%d")
        if ((strptime(ymd,format = "%y%m%d") >= strptime(s_ymd,format = "%y%m%d") & strptime(ymd,format = "%y%m%d") <= strptime(e_ymd,format = "%y%m%d")) == TRUE) {
            df$group_var[i]<-char
    }
  }
}


create_gv("example","171224","171224","D")

I get

> example
           start_time group_var
1 2017-12-24 10:42:39        NA
2 2017-12-24 10:44:31        NA
3 2018-01-14 12:05:53        NA
4 2018-01-14 12:22:12        NA

Reproducible data frame named example here:

example <- structure(list(start_time = structure(c(1514112159, 1514112271, 1515931553, 1515932532), class = c("POSIXct", "POSIXt"), tzone = ""),  group_var = c(NA, NA, NA, NA)), .Names = c("start_time", "group_var"), row.names = c(NA, -4L), class = "data.frame")

Desired output:

           start_time group_var
1 2017-12-24 10:42:39         D
2 2017-12-24 10:44:31         D
3 2018-01-14 12:05:53         NA
4 2018-01-14 12:22:12         NA

Upvotes: 0

Views: 95

Answers (1)

Naren Srinivasan
Naren Srinivasan

Reputation: 36

From your description, my understanding is that you want to check if the date in a row is between the start and end date (which are scalars), and update the value of group_var accordingly.

The lubridate package provides a set of tools which allow to easily work with dates. In order to compare dates you don't need to format them. format only helps with the viewing of these dates. I have used the dplyr package which allows you to easily perform data transformations.

To solve the problem, we use the dplyr::mutate function which transforms a column by row, as a function of other columns. In this case, the date column in our dataset (start_time) is to compared with scalar start and end times in order to codify the group_var variable.

library(lubridate)
library(magrittr)

char <- "D"
# Randomly setting the start and end times for the purpose of the example. Any value can be passed to this.
s_ymd <- df$start_time[1] - 5000
e_ymd <- df$start_time[2] + 5000

df %>% dplyr::mutate(group_var = ifelse(start_time > s_ymd & start_time < 
                                         e_ymd,
                                         char, NA)) -> df
df

To use a function directly, write:

create_gv <- function(start_time, s_ymd, e_ymd, char){
    g_var <- ifelse(start_time > s_ymd & start_time < e_ymd,
                                    char, NA)
    return(g_var)
}

df %>% dplyr::mutate(group_var = create_gv(start_time, !!s_ymd, !!e_ymd, 
                                                                !!char))

Here since s_ymd, e_ymd and char are scalars (i.e. not columns in the data frame), we need to unquote them. Note that the mutate function works on vectorized functions as desired.

Upvotes: 1

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