Processing the list of data.frames with “apply” family of functions

Question

I have a data frame which I then split into three (or any number) of dataframes.

What I’m trying to do is to automatically process each column in each dataframe and add

Answer 1

Use the plyr package to do all of this one step:

library(plyr)
clag <- function(x, n=1)c(rep(NA, n), head(x, -n))
x <- ddply(dd, .(dim1), transform, 
               v1.lag=clag(v1), v2.lag=clag(v2), v3.lag=clag(v3))

head(x)
          v1         v2         v3 dim1 dim2     v1.lag     v2.lag     v3.lag
1  0.4465910 -0.2564334 -0.9122640    A    J         NA         NA         NA
2 -0.3748563 -0.9461061  0.1641274    A    J  0.4465910 -0.2564334 -0.9122640
3 -0.5010834 -0.4413026 -0.7509968    A    J -0.3748563 -0.9461061  0.1641274
4 -0.5278584 -0.6377017  0.5528831    A    J -0.5010834 -0.4413026 -0.7509968
5 -0.4290586  0.4687849  0.6885102    A    J -0.5278584 -0.6377017  0.5528831
6  0.1179935 -0.2742456 -0.1945482    A    J -0.4290586  0.4687849  0.6885102