Visualizing Tortilla Sales

Open Produce has been really rigorous about keeping good point-of-sale data over the past 4 months, so looking back we can now tease out some interesting patterns in buying habits.

Certain things that “go together” frequently get bought on the same ticket. If you look back over tickets and count up how many times each pair of items is bought together, you can get a sense of how related any two items we sell are. Mathematically you can look at this as a weighted graph. For example, here is a picture of one such graph (circles correspond to items, and the closer two circles are, the more frequently those items are bought together.)

(Click image for larger size; other formats: [svg] [graphviz])

Corn tortillas are a daily staple for many Mexicans and Latin Americans. We sell the best fresh corn tortillas in Chicago, El Milagro brand, for a good price in packs of 12. They’re good, so many people buy a single pack now and again, even if they’re not staple eaters. However, we also have a discount for people who buy 3 packs at a time, and many staple eaters purchase as many as 9 or 12 packs per day.

This graph shows some interesting patterns. Both 1-pack and 3-pack buyers also frequently buy produce that makes sense with tortillas, such as tomatoes, avocados, jalapeños, and limes—guacamole fixings—and 3-pack buyers occasionally go for bargain produce. However, 3-pack buyers also frequently buy well-known Mexican products such as the medio litro size of Mexican coke and de la Rosa peanut candy, while 1-pack buyers do so less. Also, 1-pack buyers buy slightly more canned beans than 3-pack buyers. In particular 1-pack buyers purchase canned refried beans while 3-pack buyers rarely do. Finally note that 1-pack buyers sometimes purchase prepared foods such as mtr meals and clif bars, while 3-pack buyers generally don’t.

My reading of this is that staple tortilla eaters mostly buy fresh produce and a couple Mexican products, while non-staple eaters buy slightly more prepared food, less produce, and fewer Mexican products. If you’re a Mexican immigrant who eats refried beans every day, maybe you feel weirder about seeing them in a can and make them better, for cheaper, at home; if you’re a grad student on taco night, maybe you grab the can. Or maybe we just don’t carry the right kind of refried beans—La Preferida makes about a dozen kinds, and we carry only one size of the vegetarian kind. Staple tortilla eaters almost certainly have more specific bean preferences!

What’s clear is that there are two distinct categories of customers here who interact with one item we sell in very different ways. Tortillas are a crucial crossover point for staple eaters and exotic eaters to try new things. How can we get 1-pack buyers to buy avocados as frequently as 3-pack buyers? It’s a shocking thought, but do 1-pack buyers perhaps not know how awesome avocados are? And what other products do 3-pack buyers want—better beans, or something else like the de la Rosa candy?