R_how can I use str_sub to split date and time - r

Question

The following file names were used in a camera trap study. The S number represents the site, P is the plot within a site, C is the camera number within the plot, the first string of numbers is the YearMonthDay and the second string of numbers is the HourMinuteSecond.
file.names <- c( 'S123.P2.C10_20120621_213422.jpg',
'S10.P1.C1_20120622_050148.jpg',
'S187.P2.C2_20120702_023501.jpg')
file.names
Use a combination of str_sub() and str_split() to produce a data frame with columns corresponding to the site, plot, camera, year, month, days, hour, minute, and second for these three file names. So we want to produce code that will create the data frame:
Site
Plot
Camera
Year
Month
Day
Hour
Minute
Second
S123
P2
C10
2012
06
21
21
34
22
S10
P1
C1
2012
06
22
05
01
48
S187
P2
C2
2012
07
02
02
35
01
My codes are below:
file.names %>%
str_sub(start = 1, end = -5) %>%
str_replace_all("_", ".") %>%
str_split(pattern = fixed("."), n = 5)
I have no idea how to split date and time

Answer 1

nms <- c("Site", "Plot", "Camera", "Year", "Month", "Day", "Hour", "Minute", "Second")
library(tidyverse)
data.frame(file.names) %>%
extract(file.names, nms,
'(\\w+)\\.(\\w+)\\.(\\w+)_(\\d{4})(\\d{2})(\\d{2})_(\\d{2})(\\d{2})(\\d{2})')
Site Plot Camera Year Month Day Hour Minute Second
1 S123 P2 C10 2012 06 21 21 34 22
2 S10 P1 C1 2012 06 22 05 01 48
3 S187 P2 C2 2012 07 02 02 35 01
in Base R:
type.convert(strcapture('(\\w+)\\.(\\w+)\\.(\\w+)_(\\d{4})(\\d{2})(\\d{2})_(\\d{2})(\\d{2})(\\d{2})',
file.names, as.list(setNames(character(length(nms)), nms))), as.is = TRUE)
Site Plot Camera Year Month Day Hour Minute Second
1 S123 P2 C10 2012 6 21 21 34 22
2 S10 P1 C1 2012 6 22 5 1 48
3 S187 P2 C2 2012 7 2 2 35 1

Answer 2

This is a specific case where your data is pretty neatly formatted with fields separated by either _ or ., and where the date and time fields have uniform character length. That means you can skip doing regex and instead just split by those delimeters, drop the substrings into a data frame, then separate the date components and the time components by their positions. As is often the case, as a tidyverse solution you're trading writing extra code for it being pretty easy to follow and scale.
library(magrittr)
strsplit(file.names, split = "[._]") %>%
purrr::map_dfr(setNames, c("site", "plot", "camera", "date", "time", "ext")) %>%
tidyr::separate(date, into = c("year", "month", "day"), sep = c(4, 6)) %>%
tidyr::separate(time, into = c("hour", "minute", "second"), sep = c(2, 4)) %>%
dplyr::select(-ext)
#> # A tibble: 3 × 9
#> site plot camera year month day hour minute second
#> <chr> <chr> <chr> <chr> <chr> <chr> <chr> <chr> <chr>
#> 1 S123 P2 C10 2012 06 21 21 34 22
#> 2 S10 P1 C1 2012 06 22 05 01 48
#> 3 S187 P2 C2 2012 07 02 02 35 01
The ext column was leftover from the initial string splitting, so you can drop it.

Answer 3

I don't know anything about str_sub or str_split other than the fact that they may be efforts to adapt the sub and strsplit functions to an alternate universe. I just learned base R and have not really seen the need to learn a new syntax. Here's a base solution:
as.POSIXct( sub( "([^_]+[_])(\\d{8})[_](\\d{6})", "\\2 \\4", file.names) , format="%Y%m%d %H%M%S")
[1] "2012-06-21" "2012-06-22" "2012-07-02"
You can real the sub pattern as
1) beginning with the start of the string collect all the non-underscore characters into the first capture group
2) Then get the next 8 digits (if they exist) in a second capture group
3) and everything that follows will be in a third capture group
The substitution is to just return the contents of the second capture group. The conversion to Date values is straightforward. I'm assuming that should be clear from the code, but if not then see ?as.Date.
Here's the rest;
as.POSIXct( sub( "([^_]+[_])(\\d{8})[_](\\d{6})(.+$)", "\\2 \\3", file.names) ,
format="%Y%m%d %H%M%S")
[1] "2012-06-21 21:34:22 PDT" "2012-06-22 05:01:48 PDT" "2012-07-02 02:35:01 PDT"
If you want the break out then convert to POSIXlt and extract the resulting list.