For the record, for
x = "TGAGGTAGTAGTTTGTGCTGTTAT
TAGTAGTTTGTGCTGTTA
TGAGGTAGTAGTTTGTAC
TGAGAACTGAATTCCATAGG"
a Biostrings solution is
library(Biostrings)
consensusMatrix(DNAStringSet(strsplit(x, "\n")[[1]]))
which will be fast for millions of sequences.
solved frequency of letters at position in string [closed]