Building a comma delimited string from Cell Range

I would like to build a comma-delimited string from a range of cells. I would like to be able to put a number in the cell next to the word to indicate whether or not to include the cell in the string. Once there is a number entered in column b, I would like to sort on column b.

For example,

word1 1
word2 2
word3 3
word4

I need a function to build a string to look like "word1,word2,word3"

Thanks,

g