R: Loop function over columns in a R script

Question

Assume we have following table where we have each two pairs of variables to be tested with each other (the original table has far more columns):http://pastebin.com/igeMTaSB

How can I create a loop in R so that it applies a function each one or two rows in a script?

Example Code:

library(urca)
library(lmtest)

# Load data (See link)

table = read.csv("test.csv", header = TRUE, sep=",")
table = data.frame(table)
table

# For each column in the table (a1-d2), do
VARselect(table$column,lag.max = 10,type="both")

# For each two sequent pairs in the table (a1+a2, b1+b2,c1+c2,d1+d2), do
grangertest(table$a1, table$a2, order = 1, na.action = na.omit)

For the one variable case, use sapply or lapply: lapply(table, function(i) VARselect(i,lag.max = 10,type="both")). — lmo
– lmo, Commented Jun 24, 2016 at 12:13

lmo · Accepted Answer · 2016-06-24 12:17:13Z

1

For the one variable case, use sapply or lapply, for example:

myVarSel <- lapply(table, function(i) VARselect(i,lag.max = 10,type="both"))

If your pairs of variables are located adjacently (columns 1,2 and 3,4 and 5,6), you can use lapply as follows:

myGtests <- lapply(seq(1, 5, 2), function(i) grangertest(table[[i]], table[[i+1]], order = 1,
                                             na.action = na.omit))

If the variables are arranged in a different manner, you can use tools like grep on the names(df) to locate them. for extraction in lapply.

The lapply function returns a list, where each element is the result of the corresponding function.

answered Jun 24, 2016 at 12:17

lmo

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