laf_open: Create a connection to a file using a data model.

Description

Uses a data model to create a connection to a file. The data model contains all the information needed to open the file (column types, column widths, etc.).

Usage

laf_open(model, ...)

Value

Object of type laf. Values can be extracted from this object using indexing, and methods such as read_lines, next_block.

Arguments

model: a data model, such as one returned by read_dm or detect_dm_csv.
...: additional arguments can be used to overwrite the values specified by the data model. These are listed in the argument documentation for laf_open_csv and laf_open_fwf, e.g. see ignore_failed_conversion.

Details

Depending on the field `type' laf_open uses laf_open_csv and laf_open_fwf to open the file. The data model should contain all information needed by these routines to open the file.

Examples

Run this code

# Create some temporary files
tmpcsv  <- tempfile(fileext="csv")
tmp2csv <- tempfile(fileext="csv")
tmpyaml <- tempfile(fileext="yaml")

# Generate test data
ntest <- 10
column_types <- c("integer", "integer", "double", "string")
testdata <- data.frame(
    a = 1:ntest,
    b = sample(1:2, ntest, replace=TRUE),
    c = round(runif(ntest), 13),
    d = sample(c("jan", "pier", "tjores", "corneel"), ntest, replace=TRUE)
    )
# Write test data to csv file
write.table(testdata, file=tmpcsv, row.names=FALSE, col.names=FALSE, sep=',')

# Create LaF-object
laf <- laf_open_csv(tmpcsv, column_types=column_types)

# Write data model to file
write_dm(laf, tmpyaml)

# Read data model and open file
laf <- laf_open(read_dm(tmpyaml))

# Write test data to second csv file
write.table(testdata, file=tmp2csv, row.names=FALSE, col.names=FALSE, sep=',')

# Read data model and open second file, demonstrating the use of the optional
# arguments to laf_open
laf2 <- laf_open(read_dm(tmpyaml), filename=tmp2csv)

# Cleanup
file.remove(tmpcsv)
file.remove(tmp2csv)
file.remove(tmpyaml)