ESA 2013

I'm about to head to Minneapolis for a week to attend the annual meeting of the Ecological Society of America, the first I've attended. Here's where I'll be participating:

• I'm an instructor at a Software Carpentry workshop for ecologists on Sunday along with Ethan White and assisted by Elita Baldridge. It's a condensed, 1-day workshop (instead of the typical 2) and we'll focus on using the shell, regular expressions, and version control. I'll be teaching about Git and GitHub and how they can benefit ecologists
• I'm giving a 5-minute "Ignite" talk on Tuesday morning (a 5-minute talk with 20 slides that advance automatically every 15 seconds) about the EcoData Retriever (recently published in PLoS ONE).
• I'll be staffing the Dryad booth in the exhibit area during some of the exhibit/poster sessions and breaks. Come talk to me about archiving your data and learn about how your journal can integrate Dryad into the article submission and review process.

The other members of Weecology (my former lab group at Utah State) will be doing some interesting things this year as well - check the link for details.

iEvoBio 2013

I attended iEvoBio in beautiful Snowbird, UT last week. iEvoBio is a satellite conference to the larger annual Evolution meeting that lasts for two days and focuses more explicitly on informatics (although apparently Evolution now has its own informatics session.) I presented a software demo of PhyloCommons, which is now in an alpha release. I got some great feedback on usability and have a clear direction forward. Here are my brief, unorganized impressions of the conference:

• No one is sure what the "i" stands for. It's like the "i" in iPhone, right? So what the hell does that i stand for??
• There was representation from a wide array of informatics initiatives and labs. EOL, iDigBio, and BiSciCol seem very promising, and before the conference I hadn't even heard of the latter two. Among many peoples' favorite talks was by Xiao Xiao (of Weecology at Utah State), which was on using big data to test macroecological theory - very different from most of the other talks, but really interesting and very well-suited for this audience (Xiao even won a travel award for having one of the top student talks! Pretty awesome for someone who probably doesn't consider herself an evolutionary biologist.)
• There were some common themes that came up repeatedly in talks, giving a clear idea on what many people have independently decided are pressing problems in biodiversity informatics. Using and linking identifiers is a big one.
• The number of attendees was fairly small: Arlin Stolzfus says he counted 40 on the first day. There was a very unfortunate clash with some Evolution phylogenetics sessions - which most iEvoBio attendees are interested in. The second day had more, although I didn't count how many.
• The afternoon of the second day was set aside for Birds of a Feather sessions, where participants broke into small groups and discussed topics of mutual interest, then reported back. It was great to be able to interact on a more personal level with other attendees. The downside is that people tend to be interested in hard problems, the kind that aren't resolvable in an hour of discussion - so the conclusion coming out of many groups perhaps wasn't as satisfying as people had hoped it would be going in. I suppose that's unavoidable due to the nature of these hard problems. Still, these were very enlightening discussions.
• This was only my second conference. I was surprised to find that some people gave a talk at Evolution, a talk at iEvoBio, and a software demo at iEvoBio, on the same or similar topics. For some reason, I had assumed that you had to pick one. I'll look to be more actively involved in future conferences I attend.
• There was a lot of talk about gender diversity in science - highlighting a setting with a roughly equal gender split, and in which the 6-person organizing committee and two keynote speakers consist entirely of women. An interesting comment that came out of a BOAF group on the topic was to avoid the all-too-common conflation of "womens' issues in science" with when to start a family, etc. Three problems with this: (A) not all women are looking to have kids soon (or possibly ever) so these discussions are irrelevant to these women (who, of course, have plenty of other issues they'd probably like to discuss); (B) these are parents' issues in science, not womens' issues - plenty of men take an active role in the raising of their children; and (C) this only serves to perpetuate unfortunate stereotypes of "women as baby factories" and therefore is counter-productive.
• Carol and 2-year-old Ruben got to come with me, which was great! They played at Snowbird on day 2 and we hung out in Utah for an extra day before returning home. Pro tip: never, ever, choose the red-eye flight when flying with a toddler. Not worth the $100 savings. To make things even worse, our flight was delayed a full hour.
• Snowbird is beautiful, and I had a nice chance to return home. Next year it'll be in Raleigh, NC, so I'll certainly be attending.

A simple Python phylopic.org wrapper

PhyloPic.org is an online repository of species silhouettes. I love the idea, I think it could be very useful to jazz up figures, and they have a fantastic search feature and API. This morning I wrote up a simple Python wrapper of the API - enter one or more taxon names, download thumbnail images for each one.

In [1]:

import phylopic

phylopic.download_pics('Turdus migratorius', 'Anolis carolinensis', 'Panthera leo', img_format='thumb.png')

Downloading pic for Turdus migratorius... done!
Downloading pic for Anolis carolinensis... done!
Downloading pic for Panthera leo... done!

In [2]:

imshow(imread('Turdus migratorius.thumb.png'))

Out[2]:

<matplotlib.image.AxesImage at 0x37a6c10>

In [3]:

imshow(imread('Anolis carolinensis.thumb.png'))

Out[3]:

<matplotlib.image.AxesImage at 0x36cf250>

In [4]:

imshow(imread('Panthera leo.thumb.png'))

Out[4]:

<matplotlib.image.AxesImage at 0x36fc9d0>

Currently you can download either a low-res thumbnail or an SVG (the default, not so ugly and pixel-y, but I couldn't find a good way to embed it into an IPython notebook.)

Code available on GitHub

Blogging with IPython: distances in higher dimensions

This is my first experiment blogging with an iPython notebook, which allows easily embedding interpreted code and figures. I've found this to be a fun and convenient way to write up blog posts that might contain some technical ideas or data, potentially turning this blog into an open lab notebook. Most of this is just me toying around and experimenting with probability distributions; it may or may not be new to you.

The question

As part of a research idea I'm playing with, I'm thinking about characterizing "average members" of populations where several traits are measured, as well as the average difference between two individuals in a population.

Let's assume for simplicity that we're dealing with normally distributed functional traits. Many traits in nature happen to be approximately normally distributed; the central limit theorem also guarantees that means of many aggregate measures tend to approach normality. If you measure the trait values for many individuals, you'll get a distribution like this:

In [1]:

import scipy.stats as s
data = s.norm(0,1).rvs(100000)
hist(data, 100)
show()

The mean of this distribution is zero. But what is the average distance from the center? It's not zero; that's the minimum distance from the center. The average distance for this data is:

In [2]:

hist(abs(data), 100)
show()

In [3]:

mean(abs(data))

Out[3]:

0.79749462465259524

...about 0.8.

Now, what happens as I increase the number of dimensions? Let's assume that we're measuring two independent traits in each individual, both normally distributed. This becomes a two-dimensional Gaussian distribution, with its peak in the center:

In [4]:

data = s.norm(0,1).rvs((2, 100000))

hexbin(data[0], data[1])
cbar = colorbar()
cbar.set_label('point density')

So, what is the average distance from the center now?

In [5]:

mean([(x**2 + y**2) ** 0.5 for x, y in zip(data[0], data[1])])

Out[5]:

1.2517969486248142

As the number of dimensions increases, the average distance from the center also increases. It's hard to visualize this as the number of dimensions continue to increase, but it turns out the average distance from the center increases predictably, with the square root of the number of dimensions.

In [6]:

import random

MAX_DIMENSIONS = 200

avg_distances = []
for d in range(1, MAX_DIMENSIONS):
    data = s.norm(0,1).rvs((d, 100))
    distances = [sum([x**2 for x in point])**0.5 for point in zip(*data)]
    avg_distances.append(mean(distances))
    
xs = range(1, MAX_DIMENSIONS)
ys = avg_distances

scatter(log(xs), log(ys))

m, b, r, p, se = s.linregress(log(xs), log(ys))

print 'slope=%s, intercept=%s, r^2=%s' % (m, b, r**2)

plot([min(log(xs)), max(log(xs))], [b+min(log(xs))*m, b+max(log(xs))*m])
xlabel('no. dimensions')
ylabel('avg. distance from center')
    
show()

slope=0.516456510273, intercept=-0.0787972583541, r^2=0.998092351213

We've looked at the "average" member of a population. My next question is, what is the average difference between two members of the population?

In one dimension and two dimensions:

In [7]:

data = s.norm(0,1).rvs((2, 100000))

hist(abs(data[0] - data[1]), 100)
show()

In [8]:

mean(abs(data[0] - data[1]))

Out[8]:

1.1254983464319279

In [9]:

d = 2
data = s.norm(0,1).rvs((2, d, 100000))

distances = [sum([x**2 for x in point]) ** 0.5 for point in zip(*(data[0] - data[1]))]
hist(distances, 100)
show()

In [10]:

mean(distances)

Out[10]:

1.7730613234364447

And finally, how does this change as the number of dimensions increases?

In [11]:

avg_distances = []

for d in range(1, MAX_DIMENSIONS):
    data = s.norm(0,1).rvs((2, d, 100))
    
    distances = [sum([x**2 for x in point]) ** 0.5 for point in zip(*(data[0] - data[1]))]
    avg_distances.append(mean(distances))

xs = range(1, MAX_DIMENSIONS)
ys = avg_distances

scatter(log(xs), log(ys))

m, b, r, p, se = s.linregress(log(xs), log(ys))

print 'slope=%s, intercept=%s, r^2=%s' % (m, b, r**2)

plot([min(log(xs)), max(log(xs))], [b+min(log(xs))*m, b+max(log(xs))*m])
xlabel('no. dimensions')
ylabel('avg. distance between two individuals')
    
show()

slope=0.516526929956, intercept=0.268035406832, r^2=0.998039284826

The mean distance between two individuals also seems to increase with the square root of the number of dimensions and seems to be between one and two times the average distance from the center.

Conclusions

IPython notebooks let me write some fast Python code to explore something I'm curious about in minutes and post the whole thing to a blog instantly. Very cool, and I'm going to keep using this in the future. I wish I hadn't put off trying this out for so long.