Drop the specific files in the filelist by conditions

[nchan08]

I have time series data as follow:

L1_0101_0601_A L1_0101_0603_A L1_0101_0605_B L1_0101_0608_B L1_0101_0610_C L1_0101_0612_C L1_0101_0615_A L1_0101_0617_A L1_0101_0619_A L1_0101_0622_B L1_0101_0624_B L1_0101_0626_C L1_0101_0629_C L1_0101_0631_A L1_0101_0633_A L1_0101_0635_B L1_0101_0638_B L1_0101_0640_C L1_0101_0642_C L1_0101_0645_A L1_0101_0647_A L1_0101_0649_A and so on.

library(tidyverse)

filelist <- c("L1_0101_0601_A", "L1_0101_0603_A", "L1_0101_0605_B", 
"L1_0101_0608_B", "L1_0101_0610_C", "L1_0101_0612_C",
"L1_0101_0615_A", "L1_0101_0617_A", "L1_0101_0619_A",
"L1_0101_0622_B", "L1_0101_0624_B", "L1_0101_0626_C",
"L1_0101_0629_C")

I want to keep the files conditionally. For example, in the above filelist, I want to keep only two continuous files ending A, B and C. In the filelist, sometimes, there are three continuous files ending A or B or C. So, I want to drop "L1_0101_0619_A" and "L1_0101_0649_A" because it is the third files ending A. I will keep other twos. Like this, there are several files which I would like to remove.

Anyone can help me?

[technocrat]

This solution is strictly constrained by the data provided in which no more than three continuous files ending in the same letter occur.

filelist <- c("L1_0101_0601_A", "L1_0101_0603_A", "L1_0101_0605_B", 
              "L1_0101_0608_B", "L1_0101_0610_C", "L1_0101_0612_C",
              "L1_0101_0615_A", "L1_0101_0617_A", "L1_0101_0619_A",
              "L1_0101_0622_B", "L1_0101_0624_B", "L1_0101_0626_C",
              "L1_0101_0629_C")

pat <- "^L1_\\d{4}_\\d{4}_"

# only last character is used
(shortlist <- gsub(pat,"",filelist))
#>  [1] "A" "A" "B" "B" "C" "C" "A" "A" "A" "B" "B" "C" "C"

# find the index locations of sequential occurrences
(runs <- rle(shortlist))
#> Run Length Encoding
#>   lengths: int [1:6] 2 2 2 3 2 2
#>   values : chr [1:6] "A" "B" "C" "A" "B" "C"

# find the indexes locations of the third occurrence
(drops <- cumsum(runs$lengths)[which(runs$lengths > 2)])
#> [1] 9

# use this to subset out excess occurrence
(pruned <- filelist[-9])
#>  [1] "L1_0101_0601_A" "L1_0101_0603_A" "L1_0101_0605_B" "L1_0101_0608_B"
#>  [5] "L1_0101_0610_C" "L1_0101_0612_C" "L1_0101_0615_A" "L1_0101_0617_A"
#>  [9] "L1_0101_0622_B" "L1_0101_0624_B" "L1_0101_0626_C" "L1_0101_0629_C"

# wrap in a function

trim_to_two <- function(x) {
  runs = rle(gsub("^L1_\\d{4}_\\d{4}_","",x))
  return(cumsum(runs$lengths)[which(runs$lengths > 2)] * -1)
  }

(pruned <- filelist[trim_to_two(filelist)])
#>  [1] "L1_0101_0601_A" "L1_0101_0603_A" "L1_0101_0605_B" "L1_0101_0608_B"
#>  [5] "L1_0101_0610_C" "L1_0101_0612_C" "L1_0101_0615_A" "L1_0101_0617_A"
#>  [9] "L1_0101_0622_B" "L1_0101_0624_B" "L1_0101_0626_C" "L1_0101_0629_C"

# modify input to introduce a second repetition of three

filelist <- c("L1_0101_0601_A", "L1_0101_0603_A", "L1_0101_0605_A", 
              "L1_0101_0608_B", "L1_0101_0610_C", "L1_0101_0612_C",
              "L1_0101_0615_A", "L1_0101_0617_A", "L1_0101_0619_A",
              "L1_0101_0622_B", "L1_0101_0624_B", "L1_0101_0626_C",
              "L1_0101_0629_C")

(pruned <- filelist[trim_to_two(filelist)])
#>  [1] "L1_0101_0601_A" "L1_0101_0603_A" "L1_0101_0608_B" "L1_0101_0610_C"
#>  [5] "L1_0101_0612_C" "L1_0101_0615_A" "L1_0101_0617_A" "L1_0101_0622_B"
#>  [9] "L1_0101_0624_B" "L1_0101_0626_C" "L1_0101_0629_C"

Created on 2023-01-16 with reprex v2.0.2

[nchan08]

@technocrat Thank you so much! It works perfectly.