Counting letters before and after a letter - r

Question

I have an excel file of a list of sequences. How would I go about getting the number of times a letter appears before a letter in square brackets? An example of an entry is below.
GTCCTGGTTGTAGCTGAAGCTCTTCCC[A]CTCCTCCCGATCACTGGGACGTCCTATGT
I'd also like to do this for the letter after the square brackets.
Edit: Apologies for the confusion. Take the example below. Id like to count how many times A, C, G, and T appears immediately before and after the letter in square brackets (for which there is only one per line). So to count the occurences of A[A]A, A[A]C, C[A]A, and so on. The file is in excel, and I'm happy to use any method in excel, R or in Linux.
CCCACCCGCCAGGAAGCCGCTATCACTGTCCAAGTTGTCATCGGAACTCC[A]CCAGCCTGTGGACTTGGCCTGGTGCCGCCCATCCCCCTTGCGGTCCTTGC
ACCACTACCCCCTTCCCCACCATCCACCTCAGAAGCAGTCCCAGCCTGCC[A]CCCGCCAGCCCCTGCCCAGCCCTGGCTTTTTGGAAACGGGTCAGGATTGG
TTTGCTTTAAAATACTGCAACCACTCCAGGTAAATCTTCCGCTGCCTATA[A]CCCCGCCAATGAGCCTGCACATCAGGAGAGAAAGGGAAGTAACTCAAGCA
GAAATCTTCTGAAACAGTCTCCAGAAGACTGTCTCCAAATACACAGCAGA[A]CCAGCCAGTCCACAGCACTTTACCTTCTCTATTCTCAGATGGCAATTGAG
GGACTGCCCCAAGGCCCGCAGGGAGGTGGAGCTGCACTGGCGGGCCTCCC[A]GTGCCCGCACATCGTACGGATCGTGGATGTGTACGAGAATCTGTACGCAG
GGCCCAACGCCATCCTGAAACTCACTGACTTTGGCTTTGCCAAGGAAACC[A]CCAGCCACAACTCTTTGACCACTCCTTGTTATACACCGTACTATGTGGGT
TCTGCCTGGTCCGCTGGAGCTGGGCATTGAAGCCCCGCAGCTGCTCAGCC[A]CCTGCCCCGCCATCAAGAAGGCCCCACCGGCCCTGGGAAGGACACCCCTG
TTTGAAGCCCTTATGAACCAAGAAACCTTCGTTCAGGACCTCAAAATCAA[A]CCCCGCCACATGCAGCTCGCAGGCCTGCAGGAGGAAAGACAGGTTAGCAA
CTGCAGCCTACCTGTCCATGTCCCAGGGGGCCGTTGCCAACGCCAACAGC[A]CCCCGCCGCCCTATGAGCGTACCCGCCTCTCCCCACCCCGGGCCAGCTAC
ACTGGCAAACATGTTGAGGACAATGATGGAGGGGATGAGCTTGCATAGGA[A]CCTGCCGTAGGGCCACTGTCCCTGGAGAGCCAAGTGAGCCAGCGAGAAGG
CACCCTCAGAGAAGAAGAAAGGAGCTGAGGAGGAGAAGCCAAAGAGGAGG[A]GGCAGGAGAAGCAGGCAGCCTGCCCCTTCTACAACCACGAGCAGATGGGC
CCAGCCCTGTATGAGGACCCCCCAGATCAGAAAACCTCACCCAGTGGCAA[A]CCTGCCACACTCAAGATCTGCTCTTGGAATGTGGATGGGCTTCGAGCCTG
TTCCTGTGCGCCCCAACAACTCCTTTAGCTGGCCTAAAGTGAAAGGACGG[A]CCTGCCAATGAAAATAGACTTTCAGGGTCTAGCAGAAGGCAAGACCACCA
CTAACACCCGCACGAGCTGCTGGTAGATCTGAATGGCCAAGTCACTCAGC[A]CCTGCCGATACTCAGCCAGGTCAAAATTGGTGAGGCAGTGTTCATTCTGG
AGTTCTGCATCTGGAGCAAATCCTTGGCACTCCCTCATGCTGGCTATCAC[A]CCTGCCACGAATGTGCCATGGCCCAACCCTGCAGTCCATAAAGAAAACAA
CGTGCCCATGCAGCTAGTGCTCTTCCGAGAGGCTATTGAACACAGTGAGC[A]CCTGCCACGCCTATCCCCTTCCCCATCATCTCAGTGATGGGGTATGTCTA
ACAAGGACCTGGCCCTGGGGCAGCCCCTCAGCCCACCTGGTCCCTGCCTT[A]CCCAGCCAGTACTCTCCATCAGCACGGCCGAAGCCCAGCTTGTAGTCATT

Answer 1

You could split the original string into parts. From the start of the string to the first [ and from the first ] to the end of the string.
int count = firstPart.Count(f => f == 'a');
count += secondPart.Count(f => f == 'a');

Answer 2

Option Explicit
Sub test()
Dim seq As String
seq = "GTCCTGGTTGTAGCTGAAGCTCTTCCC[A]CTCCTCCCGATCACTGGGACGTCCTATGT"
Debug.Print CountLetter("A", seq)
End Sub
Function CountLetter(letter As String, ByVal sequence As String) As Long
'--- assumes the letter in the brackets is the same as that being counted
Dim allLetters() As String
allLetters = Split("A,C,G,T", ",")
Dim letterToDelete As Variant
For Each letterToDelete In allLetters
If letterToDelete <> letter Then
sequence = Replace(sequence, letterToDelete, "")
End If
Next letterToDelete
CountLetter = Len(sequence) - 1
End Function

Answer 3

x = "GTCCTGGTTGTAGCTGAAGCTCTTCCC[A]CTCCTCCCGATCACTGGGACGTCCTATGT"
#COUNT 'A'
sapply(unlist(strsplit(x,"\\[[A-z]\\]")), function(a) length(unlist(gregexpr("A", a))))
# GTCCTGGTTGTAGCTGAAGCTCTTCCC CTCCTCCCGATCACTGGGACGTCCTATGT
# 3 4
#COUNT 'G'
sapply(unlist(strsplit(x,"\\[[A-z]\\]")), function(a) length(unlist(gregexpr("G", a))))
# GTCCTGGTTGTAGCTGAAGCTCTTCCC CTCCTCCCGATCACTGGGACGTCCTATGT
# 7 6

Answer 4

New R solution (after clarification by OP)
Let's assume the data have been read from Excel into a data.table called los (list of sequences) which has only one column called sequence. Then, the occurences can be counted as follows:
library(data.table)
los[, .N, by = stringr::str_extract(sequence, "[ACGT]\\[[ACGT]\\][ACGT]")]
# stringr N
#1: C[A]C 8
#2: A[A]C 5
#3: C[A]G 1
#4: G[A]G 1
#5: G[A]C 1
#6: T[A]C 1
str_extract() looks for one of the letters A, C, G, T followed by [ followed by one of the letters A, C, G, T followed by ] followed by one of the letters A, C, G, T in column sequence and extracts the matching substrings. Then, los is grouped by the substrings and the number of occurences is counted (.N).
Data
If the Excel file is stored in CSV format then it can be read using data.table's fread() function like this
los <- fread("your_file_name.csv")
(Perhaps, some parameters to fread() might need to be adjusted for the specific file.)
However, some data already are provided in the question. These can be read as character string using fread() as well:
los <- fread("sequence
CCCACCCGCCAGGAAGCCGCTATCACTGTCCAAGTTGTCATCGGAACTCC[A]CCAGCCTGTGGACTTGGCCTGGTGCCGCCCATCCCCCTTGCGGTCCTTGC
ACCACTACCCCCTTCCCCACCATCCACCTCAGAAGCAGTCCCAGCCTGCC[A]CCCGCCAGCCCCTGCCCAGCCCTGGCTTTTTGGAAACGGGTCAGGATTGG
TTTGCTTTAAAATACTGCAACCACTCCAGGTAAATCTTCCGCTGCCTATA[A]CCCCGCCAATGAGCCTGCACATCAGGAGAGAAAGGGAAGTAACTCAAGCA
GAAATCTTCTGAAACAGTCTCCAGAAGACTGTCTCCAAATACACAGCAGA[A]CCAGCCAGTCCACAGCACTTTACCTTCTCTATTCTCAGATGGCAATTGAG
GGACTGCCCCAAGGCCCGCAGGGAGGTGGAGCTGCACTGGCGGGCCTCCC[A]GTGCCCGCACATCGTACGGATCGTGGATGTGTACGAGAATCTGTACGCAG
GGCCCAACGCCATCCTGAAACTCACTGACTTTGGCTTTGCCAAGGAAACC[A]CCAGCCACAACTCTTTGACCACTCCTTGTTATACACCGTACTATGTGGGT
TCTGCCTGGTCCGCTGGAGCTGGGCATTGAAGCCCCGCAGCTGCTCAGCC[A]CCTGCCCCGCCATCAAGAAGGCCCCACCGGCCCTGGGAAGGACACCCCTG
TTTGAAGCCCTTATGAACCAAGAAACCTTCGTTCAGGACCTCAAAATCAA[A]CCCCGCCACATGCAGCTCGCAGGCCTGCAGGAGGAAAGACAGGTTAGCAA
CTGCAGCCTACCTGTCCATGTCCCAGGGGGCCGTTGCCAACGCCAACAGC[A]CCCCGCCGCCCTATGAGCGTACCCGCCTCTCCCCACCCCGGGCCAGCTAC
ACTGGCAAACATGTTGAGGACAATGATGGAGGGGATGAGCTTGCATAGGA[A]CCTGCCGTAGGGCCACTGTCCCTGGAGAGCCAAGTGAGCCAGCGAGAAGG
CACCCTCAGAGAAGAAGAAAGGAGCTGAGGAGGAGAAGCCAAAGAGGAGG[A]GGCAGGAGAAGCAGGCAGCCTGCCCCTTCTACAACCACGAGCAGATGGGC
CCAGCCCTGTATGAGGACCCCCCAGATCAGAAAACCTCACCCAGTGGCAA[A]CCTGCCACACTCAAGATCTGCTCTTGGAATGTGGATGGGCTTCGAGCCTG
TTCCTGTGCGCCCCAACAACTCCTTTAGCTGGCCTAAAGTGAAAGGACGG[A]CCTGCCAATGAAAATAGACTTTCAGGGTCTAGCAGAAGGCAAGACCACCA
CTAACACCCGCACGAGCTGCTGGTAGATCTGAATGGCCAAGTCACTCAGC[A]CCTGCCGATACTCAGCCAGGTCAAAATTGGTGAGGCAGTGTTCATTCTGG
AGTTCTGCATCTGGAGCAAATCCTTGGCACTCCCTCATGCTGGCTATCAC[A]CCTGCCACGAATGTGCCATGGCCCAACCCTGCAGTCCATAAAGAAAACAA
CGTGCCCATGCAGCTAGTGCTCTTCCGAGAGGCTATTGAACACAGTGAGC[A]CCTGCCACGCCTATCCCCTTCCCCATCATCTCAGTGATGGGGTATGTCTA
ACAAGGACCTGGCCCTGGGGCAGCCCCTCAGCCCACCTGGTCCCTGCCTT[A]CCCAGCCAGTACTCTCCATCAGCACGGCCGAAGCCCAGCTTGTAGTCATT")
Old solution (before clarification by OP) - left here for reference
This is a solution in base R with help of the stringr package which will work with a "list" of sequences (a data.frame), any single letter enclosed in square brackets, and arbitrary lengths of the sequences. It assumes that the data already have been read from file into a data.frame which is named los here.
# create data: data frame with two sequences
los <- data.frame(
sequence = c("GTCCTGGTTGTAGCTGAAGCTCTTCCC[A]CTCCTCCCGATCACTGGGACGTCCTATGT",
"GTCCTGGTTGTAGCTGAAGCTCTTCCCACT[C]CTCCCGATCACTGGGACGTCCTATGT"))
# split sequences in three parts
mat <- stringr::str_split_fixed(los$sequence, "[\\[\\]]", n = 3)
los$letter <- mat[, 2]
los$n_before <- stringr::str_count(mat[, 1], mat[, 2])
los$n_after <- stringr::str_count(mat[, 3], mat[, 2])
print(los)
# sequence letter n_before n_after
#1 GTCCTGGTTGTAGCTGAAGCTCTTCCC[A]CTCCTCCCGATCACTGGGACGTCCTATGT A 3 4
#2 GTCCTGGTTGTAGCTGAAGCTCTTCCCACT[C]CTCCCGATCACTGGGACGTCCTATGT C 9 9
Note this code works best if there is exactly one pair of square brackets in each sequence. Any additional brackets will be ignored.
It will also work if there is more than just one letter enclosed in brackets, e.g., [GT].
I'm confessing that I'm addicted to Hadley Wickham's stringr package because I have difficulties to remember the inconsistently named base R functions for string maninpulation like strsplit, grepl, sub, match, gregexpr, etc. To understand what I mean please have a look at the Usage and See Also sections of ?grep and compare to stringr.

Answer 5

I would think that R packages for bioinformatics, such as seqinr or Biostrings, would be a good starting point. However, here's a "roll your own" solution.
First step: get your data from Excel into R. I will assume that file mydata.xlsx contains one sheet with a column of sequence and no header. You need to adapt this for your file and sheet format.
library(readxl)
sequences <- read_excel("mydata.xlsx", col_names = FALSE)
colnames(sequences) <- "sequence"
Now you need a function to extract the base in square brackets and the bases at -1 and +1. This function uses the stringr package to extract bases using regular expressions.
get_bases <- function(seq) {
require(stringr)
require(magrittr)
subseqs <- str_match(seq, "^([ACGT]+)\\[([ACGT])\\]([ACGT]+)$")
bases <- list(
before = subseqs[, 2] %>% str_sub(-1, -1),
base = subseqs[, 3],
after = subseqs[, 4] %>% str_sub(1, 1)
)
return(bases)
}
Now you can pass the column of sequences to the function to generate a list of lists, which can be converted to a data frame.
library(purrr)
sequences_df <- lapply(sequences, get_bases) %>%
map_df(as.data.frame, stringsAsFactors = FALSE)
head(sequences_df, 3)
before base after
1 C A C
2 C A C
3 A A C
The last step is to use functions from dplyr and tidyr to count up the bases.
library(tidyr)
sequences_df %>%
gather(position, letter, -base) %>%
group_by(base, position, letter) %>%
tally() %>%
spread(position, n) %>%
select(base, letter, before, after)
Result using your 17 example sequences. I would use better names than I did if I were you: base = the base in square brackets, letter = the base being counted, before = count at -1, after = count at +1.
base letter before after
* <chr> <chr> <int> <int>
1 A A 5 NA
2 A C 9 15
3 A G 2 2
4 A T 1 NA