如何从R中的给定字符串中识别字符串中重复次数最多的字符

Question

I have this problem that I don't have the smallest idea on how to approach. Imagine that you have the following string "aabccccdeddaaa". The program needs to return the most repeated consecutive character, and how many times it's repeated, one might think that it's "a" because it repeats 5 times in the string, but that's not what I'm looking for. The correct answer for my problem is "c" because even though it just repeats 4 times, it does repeat those 4 times consecutively, while "a" repeats only 3 times consecutively.

Not looking for the solution though, only for some guidance on how to start.

Answer 1

Just went ahead and did it. You need to use a combination of a few functions. The main one is rle . It counts consecutive values. The rest is just putting together some basic functions to extract the elements of rle you need.

# Which letter is repeated most
rle(unlist(strsplit("aabccccdeddaaa", "")))$values[which.max(rle(unlist(strsplit("aabccccdeddaaa", "")))$lengths)]
[1] "c"

# How many times it's repeated
max(rle(unlist(strsplit("aabccccdeddaaa", "")))$lengths)
[1] 4

Answer 2

One approach would be to split the input string at any point where the previous and following letters do not agree. Then, sort the resulting vector of parts descending to find the letter/term which appeared the most:

x <- "aabccccdeddaaa"
parts <- strsplit(x, "(?<=(.))(?!\\1)", perl=TRUE)[[1]]
parts[order(-nchar(parts), parts)][1]

[1] "cccc"

For reference, here is the vector of terms:

parts
[1] "aa"   "b"    "cccc" "d"    "e"    "dd"   "aaa"