Read Transaction Data

Reads transaction data from a file 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 a 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 for character 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.

Author

Michael Hahsler and Kurt Hornik

Examples

## 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)
#> # this is some test data
#> item1, item2
#> item1
#> item2, item3
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)
#>     items         
#> [1] {item1, item2}
#> [2] {item1}       
#> [3] {item2, item3}
## make always sure that the items were properly separated
itemLabels(tr)
#> [1] "item1" "item2" "item3"

## 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)
#> trans1 item1
#> trans2 item1
#> trans2 item2
write(data, file = "demo_single.txt")

## read demo data
tr <- read.transactions("demo_single.txt", format = "single", cols = c(1, 2))
inspect(tr)
#>     items          transactionID
#> [1] {item1}        trans1       
#> [2] {item1, item2} trans2       

## 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)
#> item_id;trans_id
#> item1;trans1
#> item1;trans2
#> item2;trans2
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)
#>     items          transactionID
#> [1] {item1}        trans1       
#> [2] {item1, item2} trans2       

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