Add 00: at start of standalone mm:ss values but not already present hh:mm:ss values in the same column in R

Question

I have the below times in a column and would like to change the standalone mm:ss values to 00:mm:ss. The final output must be numeric.

I am not sure where to start here. I think that gsub() may be an appropriate solution, but I am not sure of the syntax to only add to the standalone mm:ss values.

This is what I see in excel

Name    Section Role    Last Activity   Total Activity
A   biology Student Feb 8 at 1:08pm 18:16
B   biology Student Feb 8 at 1:37pm 3:22:10
C   biology Student Feb 8 at 10:37pm    9:51
D   biology Student Feb 8 at 11:50am    5:32:31
E   biology Student Feb 9 at 12:08pm    7:17:49
F   biology Student Feb 10 at 1:33am    12:25:41

This is what I see when I import this into R
    structure(list(Name = c("A", "B", "C", "D", "E", "F"), Section = c("biology", 
    "biology", "biology", "biology", "biology", "biology"), Role = c("Student", 
    "Student", "Student", "Student", "Student", "Student"), `Last Activity` = c("Feb 8 at 1:08pm", 
    "Feb 8 at 1:37pm", "Feb 8 at 10:37pm", "Feb 8 at 11:50am", "Feb 9 at 12:08pm", 
    "Feb 10 at 1:33am"), `Total Activity` = structure(c(-2209009440, 
    -2209063070, -2209039740, -2209055249, -2209048931, -2209030459
    ), class = c("POSIXct", "POSIXt"), tzone = "UTC")), row.names = c(NA, 
    -6L), class = c("tbl_df", "tbl", "data.frame"))

Answer 1

The following is a preliminary solution to your problem. Note that these values are not numeric since there is no number 25:12 etc. If you want to calculate on them, you may transform them do dates, eg POSIX-classes.

Data

ex <- c("20:28", 
        "18:53", 
        "25:01:00", 
        "17:55", 
        "27:04:00", 
        "24:43:00") 

Code

ex[stringr::str_count(ex, ":") == 1] <- gsub("^", 
                                            "00:",  
                                             ex[stringr::str_count(ex, ":") == 1])

Output

> ex
[1] "00:20:28" "00:18:53" "25:01:00"
[4] "00:17:55" "27:04:00" "24:43:00"

Answer 2

You can count number of character in the data and prepend '00:' if it is less than 8.

df <- data.frame(time = c("20:28", "18:53", "25:01:00", "17:55", "27:04:00", "24:43:00"))
df <- transform(df, time = ifelse(nchar(time) < 8, paste0('00:', time), time))
df

#      time
#1 00:20:28
#2 00:18:53
#3 25:01:00
#4 00:17:55
#5 27:04:00
#6 24:43:00

For the updated dataset we can turn the column Last Activity into date-time and use format .

library(lubridate)
library(dplyr)

df <- df %>%
  mutate(`Last Activity` = format(ymd_hm(paste('2020', `Last Activity`)), '%T'), 
         `Total Activity` = format(`Total Activity`, '%T'))

df
#  Name  Section Role    `Last Activity`  `Total Activity`
#  <chr> <chr>   <chr>   <chr>            <chr>           
#1 A     biology Student Feb 8 at 1:08pm  18:16:00        
#2 B     biology Student Feb 8 at 1:37pm  03:22:10        
#3 C     biology Student Feb 8 at 10:37pm 09:51:00        
#4 D     biology Student Feb 8 at 11:50am 05:32:31        
#5 E     biology Student Feb 9 at 12:08pm 07:17:49        
#6 F     biology Student Feb 10 at 1:33am 12:25:41