Compare two dates in R

date, equality, r

Solution

The following solution solved my problem: Instead of using the `Date` data type, I tried to use the `POSIXct` data type. Here is the example code for reading the tab-separated textfile after which the subsetting worked in all steps of my `for` loop:

data = read.table("data.txt", header = TRUE, sep = "\t", dec = ".", 
    colClasses =c("numeric","numeric","character","POSIXct","numeric","numeric"));
startDate = as.POSIXct("2012-07-01");
endDate = as.POSIXct("2012-07-20");
all_dates = seq(startDate, endDate, 86400); #86400 is num of seconds in a day

#the following code I'm trying to run inside a loop...
for (j in 1:length(all_dates)) {
    filterdate = all_dates[j];
    my_subset = data[data$DateTimeUTC == filterdate,]
    #now I want do do some processing on my_subset...
}

Problem

I have a tab-separated text file that I imported to R. I used the following command for the import: ``` data = read.table(soubor, header = TRUE, sep = "\t", dec = ".", colClasses =c("numeric","numeric","character","Date","numeric","numeric")) ``` When I run `str(data)` to check the data-types of my columns I get: ``` 'data.frame': 211931 obs. of 6 variables: $ DataValue : num 0 0 0 0 0 0 0 0 0 NA ... $ SiteID : num 1 1 1 1 1 1 1 1 1 1 ... $ VariableCode: chr "Sucho" "Sucho" "Sucho" "Sucho" ... $ DateTimeUTC : Date, format: "2012-07-01" "2012-07-02" "2012-07-03" "2012-07-04" ... $ Latitude : num 50.8 50.8 50.8 50.8 50.8 ... $ Longitude : num 15.6 15.6 15.6 15.6 15.6 ... ``` A reproducible sample of the first 20 rows of my data is here: ``` my_sample <- data.frame( DataValue = rep(c(0, NA, 0), c(9L, 8L, 3L)), SiteID = rep(1, 20L), VariableCode = rep("Sucho", 20L), DateTimeUTC = as.Date(c( "2012-07-01", "2012-07-02", "2012-07-03", "2012-07-04", "2012-07-05", "2012-07-06", "2012-07-07", "2012-07-08", "2012-07-09", "2012-07-10", "2012-07-11", "2012-07-12", "2012-07-13", "2012-07-14", "2012-07-15", "2012-07-16", "2012-07-17", "2012-07-18", "2012-07-19", "2012-07-20" )), Latitude = rep(50.77, 20L), Longitude = rep(15.55, 20L) ) ``` Now I want to filter my table by the date. Note that I'm running my code inside a `for` loop. First, I subset my data by 1st July 2012 and do some processing. Then, I subset my data by 2nd July and do some processing, and so on.. For example, I want to get all rows with date equal to 6th July 2012. I tried the code: ``` startDate = as.Date("2012-07-01"); endDate = as.Date("2012-07-20"); all_dates = seq(startDate, endDate, 1); #the following code I'm trying to run inside a loop... for (j in 1:length(all_dates)) { filterdate = all_dates[j]; my_subset = my_sample[my_sample$DateTimeUTC == filterdate,] #now I want do do some processing on my_subset... } ``` But the above code returns an empty dataset starting from step 7 of the loop. So, for example: ``` subset_one = my_sample[my_sample$DateTimeUTC == all_dates[6],] ``` returns: `3 obs of 6 variables`. But, for some unknown reason, the example: ``` subset_two = my_sample[my_sample$DateTimeUTC == all_dates[7],] ``` returns: `0 obs of 6 variables`. (note: I edited the above code to make my problem 100% reproducible) Any ideas what I'm doing wrong?

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