How can I use if-else statements (or a better way) to assign absolute values to days in a year (using R)?

Question

I am working with daily temperature data that I have already run through R to pull out the first and last days of each year that are above a calculated threshold unique to each city dataset.

Data is brought into R in a .csv file with columns "YR", "number_of_days", "start_date", and "end_date". I only care about the "start_date" and "end_date" columns for this calculation.

For example, if I am looking at heat extremes, the first day of the year to have a temperature above 33 degrees C is May 1st and the last day of the year to have a temperature above 33 degrees C is October 20th. I do not care what the temperatures of the days in between are, just the start and end dates.

I want to convert the "May 1st" to an absolute number to be compared to other years. Below is sample data from BakersfieldTMAXextremes data.frame:

  YR  number_of_days  start_date  end_date  
1900              27     5/22/00  10/18/00  
1901              42     6/29/01  10/22/01  
1902              76      6/7/02   9/23/02  
1903              97      5/6/03  10/18/03  
1904              98      4/8/04   9/15/04  
1905             115     5/11/05  10/10/05  
1906              90     4/20/06  10/27/06  
1907              97     5/27/07  10/10/07  
1908             107     4/11/08   9/16/08  
1909             106      5/2/09   9/23/09  
1910              89     4/18/10  10/15/10  
1911              54      5/5/11    9/4/11  
1912              51     5/31/12  10/18/12  
1913             100     4/25/13  10/18/13  
1914              78     4/19/14  10/14/14  
1915              84     5/27/15   10/8/15  
1916              73      5/5/16   9/28/16  
1917              99      6/2/17   10/8/17  
1918              81      6/2/18  10/13/18  
1919              85     5/28/19   9/26/19  
1920              61     5/17/20   9/30/20  
1921              85      6/5/21   11/3/21  
1922              91     5/14/22   9/25/22  
1923              67      5/9/23   9/17/23  
1924              91      5/8/24   9/29/24  
1925              70      5/3/25   9/24/25  
1926              84     4/25/26    9/9/26  
1927              77     4/25/27  10/20/27  
1928              88      5/5/28   10/9/28  
1929              91     5/22/29  10/23/29  
1930              86     5/23/30   10/7/30  
1931              91     4/20/31   9/26/31  
1932              82     5/11/32   10/5/32  
1933              93     5/27/33   10/7/33  
1934             101     4/20/34  10/12/34  
1935              93     5/21/35  10/11/35  
1936              85     5/10/36   9/26/36  

For example, I would like to see the first start date as 141 (because it is the 141st day out of the 365 days in a year). At this point I couldn't care less about leap years, so we'll pretend they don't exist. I want the output in a table with the "YR", "start_date", and "end_date" (except with absolute values). For the first one, I would want "1900", "141" and "291" as the output.

I've tried to do this with an if-else statement, but it seems cumbersome to do for 365 days of the year (also I am fairly new to R and only have experience doing this in MATLAB). Any help is greatly appreciated!

Answer 1

Based on this answer , you can modify your data frame as follows:

library(lubridate)
df$start_date <- yday(df$start_date)
df$end_date <- yday(df$end_date)