[R] Flattening a list of data frames

From: Lorin Hochstein <lorin_at_cs.umd.edu>
Date: Thu 10 Mar 2005 - 07:07:20 EST

Hello all,

Simple version of my problem:

I've got a list of data frames, where each data frame has the same number of columns and the same column names. I'd like to flatten the list into one large data frame. Is there an easy way to do this?

Quick example code:

a <- data.frame(x=c(1,2,3),y=c(5,7,9)
b <- data.frame(x=c(2,4,7,9),y=c(2,3,5,4))
z <- list(a,b)

# Do "something" to get the equivalent of rbind(z[[1]],z[[2]]) ???

More complex version:

My data is in this format because it's the output of a "by" statment that looks like this:

y <- by(d,list(d$StudentID,d$Assignment),gapfun)

(where gapfun is a function I've defined that takes a data frame and returns another data frame).

What I would like is to do is transform y into a data frame that has columns "StudentID", "Assignment", and the columns in the data frame returned by gapfun.

Any ideas?


Lorin Hochstein
Graduate Research Assistant
Experimental Software Engineering Group
Computer Science Department
University of Maryland, College Park

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