R –Refcards and Basic I/O Operations

While working with a large number of files for data processing, I used the following R commands for data processing. Given that everyone needs to split as well merge and append data – I am just giving some code on splitting data based on parameters , and appending data as well as merging data.

Splitting Data Based on a Parameter.

The following divides the data into subsets which contain either Male or anything else in different datasets.

Input and Subset

Note the read.table command assigns the dataset name X in R environment from the file reference (path denoted by ….)

x <- read.table(....)
rowIndx <- grep("Male", x$col)
write.table(x[rowIndx,], file="match")
write.table(x[-rowIndx,], file="nomatch")

Suppose we need to divide the dataset into multiple data sets.

X17 <- subset(X, REGION == 17)

This is prefered to the technique -

attach(X)
X17 = X[REGION == 17,]

Output

For putting the files back to the Windows environment you can use-

write.table(x,file="",row.names=TRUE,col.names=TRUE,sep=" ")

Append

Lets say you have a large number of data files ( say csv files )

that you need to append (assuming the files are in same syrycture)

after performing basic operations on them.

>setwd("C:\\Documents and Settings\\admin\\My Documents\\Data")

Note this changes the working folder to folder you want it to be,

note the double slashes which are needed to define the path

>list.files(path = ".", pattern = NULL, all.files = FALSE, full.names = FALSE,

+     recursive = FALSE, ignore.case = FALSE)

The R output would be something like below

 [1] "cal1.csv"                                     "cal2.csv"                                           

[3] "cal3.csv"                                     "cal4.csv"                                           

[5] "cal5.csv"                                     "cal6.csv"                                           

[7] "cal7.csv"                                     "cal8.csv"

Now you can use the file.append command for succesively appending the second file

to the first file.

If writing a lot of similar code is a tedium use the & (concatenate) function

in excel to create the code.Note the Formula Bar (B7=A7&C7&D7&E7)

Excel is useful because it is good in click and drag repetitive text and

concatenation is easily done.

The output would be something like

Note all data here gets appended to filecal1.csv

This should be a good starting point for you to trying out R.

For a Reference Sheet, here is an excellent reference sheet from Tom Short,

and it is aptly called the Short Refcard

(http://cran.r-project.org/doc/contrib/Short-refcard.pdf)

Note- Experienced analytics people are best served by

www.rforsasandspssusers.com

Anyways MeRRy ChRistmas !

Short Refcard