read.transactions: Read Transaction Data

Description

Reads a transaction data file from disk and creates a '>transactions object.

Usage

read.transactions(file, format = c("basket", "single"), 
                  header = FALSE, sep = "", 
                  cols = NULL, rm.duplicates = FALSE, 
                  quote = "\"'", skip = 0, 
                  encoding = "unknown")

Arguments

file

the file name or connection.

format

a character string indicating the format of the data set. One of "basket" or "single", can be abbreviated.

header

a logical value indicating whether the file contains the names of the variables as its first line.

sep

a character string specifying how fields are separated in the data file. The default ("") splits at whitespaces.

cols

For the ‘single’ format, cols is a numeric or character vector of length two giving the numbers or names of the columns (fields) with the transaction and item ids, respectively. If character, the first line of file is assumed to be a header with column names. For the ‘basket’ format, cols can be a numeric scalar giving the number of the column (field) with the transaction ids. If cols = NULL, the data do not contain transaction ids.

rm.duplicates

a logical value specifying if duplicate items should be removed from the transactions.

quote

a list of characters used as quotes when reading.

skip

number of lines to skip in the file before start reading data.

encoding

character string indicating the encoding which is passed to readLines or scan (see Encoding).

Value

Returns an object of class '>transactions.

Details

For ‘basket’ format, each line in the transaction data file represents a transaction where the items (item labels) are separated by the characters specified by sep. For ‘single’ format, each line corresponds to a single item, containing at least ids for the transaction and the item.

Examples

Run this code

# NOT RUN {
## create a demo file using basket format for the example
data <- paste(
  "# this is some test data", 
  "item1, item2", 
  "item1", 
  "item2, item3", 
  sep="\n")
cat(data)
write(data, file = "demo_basket.txt")

## read demo data (skip the comment in the first line)
tr <- read.transactions("demo_basket.txt", format = "basket", sep=",", skip = 1)
inspect(tr)
## make always sure that the items were properly separated
itemLabels(tr)

## create a demo file using single format for the example
## column 1 contains the transaction ID and column 2 contains one item
data <- paste(
  "trans1 item1", 
  "trans2 item1",
  "trans2 item2", 
  sep ="\n")
cat(data)
write(data, file = "demo_single.txt")

## read demo data
tr <- read.transactions("demo_single.txt", format = "single", cols = c(1,2))
inspect(tr)

## create a demo file using single format with column headers
data <- paste(
  "item_id;trans_id",
  "item1;trans1", 
  "item1;trans2",
  "item2;trans2", 
  sep ="\n")
cat(data)
write(data, file = "demo_single.txt")

## read demo data
tr <- read.transactions("demo_single.txt", format = "single", 
  header = TRUE, sep = ";", cols = c("trans_id","item_id"))
inspect(tr)

## tidy up
unlink("demo_basket.txt")
unlink("demo_single.txt")
# }