Vim : how to index a plain text file?

Question

Is it possible to index a plain text file (a book) in vim such as :

1. This line contains the words : London, Berlin, Paris
2. In this line, I write about :          


        

Answer 1

Here is a revised version of the function posted by Prince Goulash. This version takes a list of words as input and returns a formatted and alphabetized string of the result:

function! IndexByWord( wordlist )
    let temp_dict = {}
    for word in a:wordlist
        redir => result
        sil! exe ':g/' . word . '/#'
        redir END
        let tmp_list = split(strtrans(result),"\\^\@ *")
        let res_list = []
        call map(tmp_list, 'add(res_list,str2nr(matchstr(v:val,"^[0-9]*")))')
        let temp_dict[word]  = res_list
    endfor
    let result_list = []
    for key in sort(keys(temp_dict))
        call add(result_list, key . ' : ' . string(temp_dict[key])[1:-2])
    endfor
    return join(result_list, "\n")
endfunction

One way to call it would be:

echo IndexByWord(['word1', 'word2', 'word3', etc])

There should be no problem with having a long list of words, although in that case you would probably want to use a list variable and getting the results would of course take more time. For example:

let my_word_list = ['word1', 'word2', . . . 'word1000']
echo IndexByWord(my_word_list)