Articles by Mark Fredrickson

test_that — A brief review

July 15, 2011 | Mark Fredrickson

For the last month or so, I have been using the test_that unit testing package for R (a quick note on names: both testthat and test_that are used in the documentation. The library, as available from CRAN has no underscore, so use install.packages('testthat') to get a ... [Read more...]

Peeking inside R functions

February 6, 2011 | Mark Fredrickson

R, like all good programming languages, treats functions as first class objects. Users can create functions, pass them as arguments, and have them returned as the result of other computations. You may be familiar with passing functions as arguments if you have used the apply family of functions (i.e. ... [Read more...]

Combinadics in R

August 5, 2010 | Mark Fredrickson

A question on reminded me of some code I wrote earlier this summer. The code provides a correspondence between the natural numbers 1 to (N choose K) and all the unique K sized combinations one could draw from N items. This relationship is know as the combinadic of ... [Read more...]

Using xBalance with MatchIt

August 1, 2010 | Mark Fredrickson

In a previous post, I demonstrated how to create a propensity score matching, test balance, and analyze the outcome variable using the optmatch and RItools packages. The same strategy can be used with other matching algorithms, for example the various methods included in the MatchIt package. I’ll use the ... [Read more...]

Using Optmatch and RItools for Observational Studies

July 29, 2010 | Mark Fredrickson

I am a contributor to the optmatch and the RItools packages for R. These two packages are separate, but complimentary. Both packages provide tools for adjusting observational data to exhibit “balance” on observed covariates. In a randomized control trial, treatment and control groups should have identical distributions over all covariates, ... [Read more...]

Scoping Bugs

June 22, 2010 | Mark Fredrickson

I ran a across a strange bug in R recently. Like all the best programming languages, R treats functions as first class objects. That is to say that functions can be passed as arguments and return values from functions, named as variables, and, while not part of the strict definition ... [Read more...]

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