Articles by TszKin Julian

A handy concatenation operator

February 12, 2013 | TszKin Julian

It may be useful for you to define a concatenation operator for characters. Sometimes, I find this is more intuitive and handy than using paste0 or paste. Also, it makes your code look better when you have nested paste, e.g.paste0("Y~",paste0("z",1:3, "*x",1:3,collapse="+"). The drawback is ... [Read more...]

How to do egen (stata cmd) in R

February 12, 2013 | TszKin Julian

egen(stata cmd) compute a summary statistics by groups and store it in to a new variable. For example, the data has three variables, id, time and y, we want to compute the mean of y by for each id and then store it as a new variable mean_y. ... [Read more...]

Generating a lag/lead variables

March 11, 2012 | TszKin Julian

A few days ago, my friend asked me is there any function in R to generate lag/lead variables in a data.frame or did similar thing as _n in stata. He would like to use that to clean-up his dataset in R. In stata help manual: _n contains the ... [Read more...]

Overhead cost of a function call

October 1, 2011 | TszKin Julian

Recently, I would like to apply unit testing method to my R program. The first thing i need to chop every few lines of the code into functions so that I can test each of them. A Question comes up to my mind: What is the overhead cost of a ... [Read more...]

Call by reference in R

September 11, 2011 | TszKin Julian

Sometimes it is convenient to use “call by reference evaluation” inside an R function. For example, if you want to have multiple return value for your function, then either you return a list of return value and split them afterward or you can return the value via the argument. For ... [Read more...]

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