Replace multiple strings with multiple other strings

Question

I\'m trying to replace multiple words in a string with multiple other words. The string is \"I have a cat, a dog, and a goat.\"

However, this does not produce \"I ha

Answer 1

All solutions work great, except when applied in programming languages that closures (e.g. Coda, Excel, Spreadsheet's REGEXREPLACE).

Two original solutions of mine below use only 1 concatenation and 1 regex.

Method #1: Lookup for replacement values

The idea is to append replacement values if they are not already in the string. Then, using a single regex, we perform all needed replacements:

var str = "I have a cat, a dog, and a goat.";
str = (str+"||||cat,dog,goat").replace(
   /cat(?=[\s\S]*(dog))|dog(?=[\s\S]*(goat))|goat(?=[\s\S]*(cat))|\|\|\|\|.*$/gi, "$1$2$3");
document.body.innerHTML = str;

Explanations:

• cat(?=[\s\S]*(dog)) means that we look for "cat". If it matches, then a forward lookup will capture "dog" as group 1, and "" otherwise.
• Same for "dog" that would capture "goat" as group 2, and "goat" that would capture "cat" as group 3.
• We replace with "$1$2$3" (the concatenation of all three groups), which will always be either "dog", "cat" or "goat" for one of the above cases
• If we manually appended replacements to the string like str+"||||cat,dog,goat", we remove them by also matching \|\|\|\|.*$, in which case the replacement "$1$2$3" will evaluate to "", the empty string.

Method #2: Lookup for replacement pairs

One problem with Method #1 is that it cannot exceed 9 replacements at a time, which is the maximum number of back-propagation groups. Method #2 states not to append just replacement values, but replacements directly:

var str = "I have a cat, a dog, and a goat.";
str = (str+"||||,cat=>dog,dog=>goat,goat=>cat").replace(
   /(\b\w+\b)(?=[\s\S]*,\1=>([^,]*))|\|\|\|\|.*$/gi, "$2");
document.body.innerHTML = str;

Explanations:

• (str+"||||,cat=>dog,dog=>goat,goat=>cat") is how we append a replacement map to the end of the string.
• (\b\w+\b) states to "capture any word", that could be replaced by "(cat|dog|goat) or anything else.
• (?=[\s\S]*...) is a forward lookup that will typically go to the end of the document until after the replacement map.
  • ,\1=> means "you should find the matched word between a comma and a right arrow"
  • ([^,]*) means "match anything after this arrow until the next comma or the end of the doc"
• |\|\|\|\|.*$ is how we remove the replacement map.