Is it possible to substitute characters according to a list in Lua, like tr in Perl? For example, I would like to substitute A to B and B to A (e.g. AABBCC becomes BBAACC).
In Perl, the solution would be $str ~= tr/AB/BA/. Is there any native way of doing this in Lua? If not, I think the best solution would be iterating through the entire string, since separate substitutions need to use a special symbol to distinguish characters that were already substituted and characters that weren't.
Edit: my goal was to calculate the reverse complement of a DNA string, as described here.
string.gsub can take a table as the third argument. The table is queried for each match, using the first capture as the key, and the associated value is used as the replacement string. If the value is nil, the match is not changed.
So you can build a helper table like this:
local s = "AABBCC"
local t = {A = "B", B = "A"}
local result = string.gsub(s, "[AB]", t)
print(result)
or this same one-liner:
print((string.gsub("AABBCC", "[AB]", {A = "B", B = "A"})))
Output:
BBAACC
For a one character pattern like "[AB]", "." can work as well because whatever not found in the table won't be changed. (But I don't think that's more efficient) But for some more complicated cases, a good pattern is needed.
Here is an example from Programming in Lua: this function substitutes the value of the global variable varname for every occurrence of $varname in a string:
function expand (s)
return (string.gsub(s, "$(%w+)", _G))
end