Using latent semantic analysis to find synonyms in my Getting Things Done inbox

I try to use the Getting Things Done method to keep myself organized, but sometimes I wish that my computer could help share the load of that process. During my travels on the Internet, I discovered an algorithm called Latent Semantic Analysis (or LSA for short), which has some interesting natural language processing capabilities. I figured this would be a good application for my skills I gained from this language of the month. Let's explore my GTD inbox using this algorithm and my newfound powers of R!

Automating My GTD Workflow

The script I want will crawl through my GTD inbox and look for keywords in each entry. If an entry has a set of keywords that I have indicated belong to a certain project or context, I'll have that entry highlighted a certain way and have a keyboard shortcut or something to automatically put it in that project and tag it with the proper context. For example, if an entry has the word “MoarVM” in it, I know that it belongs in the Perl 6 project.

However, in my GTD inbox, I tend to use abbreviations and initialisms, such as Fx for Firefox, or MVM for MoarVM. I'm hoping that LSA can detect the similarties between these terms so I can find which synonyms I use in my inbox.

My GTD System

It might help a bit to understand how my GTD system works. I manage all of my GTD stuff in a private Git repo, with directories for GTD projects, someday/maybe, and reference, and files under each directory for each project and such. The inbox is in a file in the root called catch-pocket.txt 1); earlier, it was a file called until I decided that Markdown wasn't a great format for my inbox. For this exercise, we'll treat each distinct line that's ever been in my inbox as a document.

Getting the Term Matrix

Using some Git/shell fu, we can easily get our list of documents:

$ cd ~/gtd
$ git log --pretty=%h | # get each commit
  xargs -L 1 git ls-tree  | # run git-ls-tree for each commit
  perl -anE 'chomp @F; say $F[2] if $F[3] =~ /^catch-pocket/' | # extract blob IDs for inbox files
  sort | uniq |
  xargs -L 1 git show > /tmp/pockets # get contents of catch-pocket files over time
$ perl -nE 'chomp; s/^\s+|\s+$//; say' /tmp/pockets |
  sort | uniq >/tmp/uniq-pockets # trim whitespace and uniqify
$ mv /tmp/uniq-pockets /tmp/pockets
$ perl -CSAD -i -nE 'print if /(\p{Latin})/' /tmp/pockets # remove any lines that have no Latin characters

Next, I wrote a Perl script to prepare a term frequency matrix, as well as a list of terms and “documents” (distinct lines) so that I can tie matrix indices back to the original term and line. Why use Perl when I'm trying to learn how to use R? Well, because this part of the process is text processing, which Perl is really good at, and more importantly, is something I know how to do quickly and well with Perl. I'm advocate of using the right tool for the job. ;)

Now that we have the term frequency matrix, we can apply LSA!

What's LSA?

LSA is a natural language processing algorithm that can discover relationships between terms and documents, the logic being that similar documents will use similar terms, and similar terms will occur in similar documents. The algorithm itself is pretty simple; first, you run a term frequency-inverse document frequency, which sort of downplays the significance of terms that occur in a lot of the documents (ex. the, a, an), and then we run a singular value decomposition on the result. TF-IDF I understand, but I don't really understand how SVD works; from what I can tell (and please feel free to explain in the comments if you can explain better than I can!), it performs a factorization on a matrix M such that M = U * S * V where S contains the singular values for M. The singular values, as I understand, are the sort of “weights” for columns in U and rows in V. After the SVD, we drop some of the lower values in S (yielding, let's say, S'), and multiply U, S', and V together to get M', which allows us to reason about which terms or documents are similar. To check the terms' simlarity, we multiply M' * t(M'), which performs a dot product on each term row with each other term row, and gives us an idea of how similar those two terms are.

R provides SVD in the standard library, but there's a package on CRAN called irlba that peforms the SVD + drop least signficant values using a fraction of the memory that a full SVD does. It was nice to have that as an option, but after playing around, R's svd function ran in much less time.

Here's a link to the source code if you're interested in checking it out:

The Results

In my dataset, there were 5,578 distinct terms; after taking the SVD of the term matrix, I only used the most significant 3,000. Here are the terms that were most similar to MVM and Fx (the first number is the index, and the last number is the value from M' * t(M')):

  "5030" "mvm" "moarvm" "152.279151036764"
  "5111" "fx" "tab" "161.788023010342"

So MVM we were able to correlate to MoarVM, but Fx links to “tab”. For what it's worth, “Firefox” also links to “tab”. Here are some other interesting similarities the script found:

  "5354" "posix" "fileno" "218.939661907348"
  "5373" "anki" "deck" "227.89608194928"
  "5517" "swiss" "workshop" "372.105081904976"
  "5561" "man" "page" "695.458878687011"
  "5570" "blog" "post" "881.443386519827"

So not a lot of synonyms, but there is definitely a relationship between those terms! I think that these results could be improved by tweaking the number of SVD values I prune, modifying how I select terms from a document, and feeding the algorithm more data. Another thought I had was to create synthetic “polyterms” from adjacent terms, so the document “perl 6 compiler” would yield the polyterms “perl 6” and “6 compiler”. No matter what, it was really interesting to play with the algorithm and see what results it came up with!

  1. 1) I was reading Dune again when I set this system up, although in retrospect, catch pocket was a terrible name, because according to GTD, nothing should re-enter the inbox =)