Partilhar via

RxTextData: Generate Text Data Source Object

  • Artigo

Description

This is the main generator for S4 class RxTextData, which extends RxDataSource.

Usage

  RxTextData(file,  stringsAsFactors = FALSE,
             colClasses = NULL, colInfo = NULL, 
             varsToKeep = NULL, varsToDrop = NULL, missingValueString = "NA",
             rowsPerRead = 500000, delimiter = NULL, combineDelimiters = FALSE,
             quoteMark = "\"", decimalPoint = ".", thousandsSeparator = NULL,
             readDateFormat = "[%y[-][/]%m[-][/]%d]", 
             readPOSIXctFormat = "%y[-][/]%m[-][/]%d [%H:%M[:%S]][%p]",
             centuryCutoff = 20, firstRowIsColNames = NULL, rowsToSniff = 10000,
             rowsToSkip = 0, returnDataFrame = TRUE,
             defaultReadBufferSize = 10000, 
             defaultDecimalColType = rxGetOption("defaultDecimalColType"),
             defaultMissingColType = rxGetOption("defaultMissingColType"),
             writePrecision = 7, stripZeros = FALSE, quotedDelimiters = FALSE,
             isFixedFormat = NULL, useFastRead = NULL, 
             createFileSet = NULL, rowsPerOutFile = NULL,
             verbose = 0, checkVarsToKeep = FALSE,
             fileSystem = NULL, inputEncoding = "utf-8", writeFactorsAsIndexes = FALSE)

Arguments

file

character string specifying a text file. If it has an .stsextension, it is interpreted as a fixed format schema file. If the colInfo argument contains start and width information, it is interpreted as a fixed format data file. Otherwise, it is treated as a delimited text data file. See the Details section for more information on using .sts files.

returnDataFrame

logical indicating whether or not to convert the result from a list to a data frame (for use in rxReadNext only). If FALSE, a list is returned.

stringsAsFactors

logical indicating whether or not to automatically convert strings to factors on import. This can be overridden by specifying "character" in colClasses and colInfo. If TRUE, the factor levels will be coded in the order encountered. Since this factor level ordering is row dependent, the preferred method for handling factor columns is to use colInfo with specified "levels".

colClasses

character vector specifying the column types to use when converting the data. The element names for the vector are used to identify which column should be converted to which type.

  • Allowable column types are:

    • "logical" (stored as uchar),
    • "integer" (stored as int32),
    • "float32" (the default for floating point data for .xdf files),
    • "numeric" (stored as float64 as in R),
    • "character" (stored as string),
    • "factor" (stored as uint32),
    • "ordered" (ordered factor stored as uint32. Ordered factors are treated the same as factors in RevoScaleR analysis functions.),
    • "int16" (alternative to integer for smaller storage space),
    • "uint16" (alternative to unsigned integer for smaller storage space),
    • "Date" (stored as Date, i.e. float64. Not supported if useFastRead = TRUE.)
    • "POSIXct" (stored as POSIXct, i.e. float64. Not supported if useFastRead = TRUE.)

  • Note for "factor" and "ordered" types, the levels will be coded in the order encountered. Since this factor level ordering is row dependent, the preferred method for handling factor columns is to use colInfo with specified "levels".

colInfo

list of named variable information lists. Each variable information list contains one or more of the named elements given below. When importing fixed format data, either colInfo or an .sts schema file should be supplied. For such fixed format data, only the variables specified will be imported. For all text types, the information supplied for colInfooverrides that supplied for colClasses.

  • Currently available properties for a column information list are:
  • type - character string specifying the data type for the column. See colClasses argument description for the available types. If the type is not specified for fixed format data, it will be read as character data.
  • newName - character string specifying a new name for the variable.
  • description - character string specifying a description for the variable.
  • levels - character vector containing the levels when type = "factor". If the levels property is not provided, factor levels will be determined by the values in the source column. If levels are provided, any value that does not match a provided level will be converted to a missing value.
  • newLevels - new or replacement levels specified for a column of type "factor". It must be used in conjunction with the levels argument. After reading in the original data, the labels for each level will be replaced with the newLevels.
  • low - the minimum data value in the variable (used in computations using the F() function.
  • high - the maximum data value in the variable (used in computations using the F() function.
  • start - the left-most position, in bytes, for the column of a fixed format file respectively. When all elements of colInfo have "start", the text file is designated as a fixed format file. When none of the elements have it, the text file is designated as a delimited file. Specification of start must always be accompanied by specification of width.
  • width - the number of characters in a fixed-width character column or the column of a fixed format file. If widthis specified for a character column, it will be imported as a fixed-width character variable. Any characters beyond the fixed width will be ignored. Specification of width is required for all columns of a fixed format file (if not provided in an .sts file).
  • decimalPlaces - the number of decimal places.
  • index - column index in the original delimited text data file. It is used as an alternative to naming the variable information list if the original delimited text file does not contain column names. Ignored if a name for the list is specified. Should not be used with fixed format files.

varsToKeep

character vector of variable names to include when reading from the input data file. If NULL, argument is ignored. Cannot be used with varsToDrop.

varsToDrop

character vector of variable names to exclude when reading from the input data file. If NULL, argument is ignored. Cannot be used with varsToKeep.

missingValueString

character string containing the missing value code. It can be an empty string: "".

rowsPerRead

number of rows to read at a time.

delimiter

character string containing the character to use as the separator between variables. If NULL and the colInfo argument does not contain "start" and "width" information (which implies a fixed-formatted file), the delimiter is auto-sensed from the list ",", "\t", ";", and " ".

combineDelimiters

logical indicating whether or not to treat consecutive non-space (" ") delimiters as a single delimiter. Space " " delimiters are always combined.

quoteMark

character string containing the quotation mark. It can be an empty string: "".

decimalPoint

character string containing the decimal point. Not supported when useFastRead is set to TRUE.

thousandsSeparator

character string containing the thousands separator. Not supported when useFastRead is set to TRUE.

readDateFormat

character string containing the time date format to use during read operations. Not supported when useFastRead is set to TRUE. Valid formats are:

  • %c Skip a single character (see also %w).
  • %Nc Skip N characters.
  • %$c Skip the rest of the input string.
  • %d Day of the month as integer (01-31).
  • %m Month as integer (01-12) or as character string.
  • %w Skip a whitespace delimited word (see also %c).
  • %y Year. If less than 100, centuryCutoff is used to determine the actual year.
  • %Y Year as found in the input string.
  • %%, %[, %] input the %, [, and ] characters from the input string.
  • [...] square brackets within format specifications indicate optional components; if present, they are used, but they need not be there.

readPOSIXctFormat

character string containing the time date format to use during read operations. Not supported when useFastRead is set to TRUE. Valid formats are:

  • %c Skip a single character (see also %w).
  • %Nc Skip N characters.
  • %$c Skip the rest of the input string.
  • %d Day of the month as integer (01-31).
  • %H Hour as integer (00-23).
  • %m Month as integer (01-12) or as character string.
  • %M Minute as integer (00-59).
  • %n Milliseconds as integer (00-999).
  • %N Milliseconds or tenths or hundredths of second.
  • %p Character string defining 'am'/'pm'.
  • %S Second as integer (00-59).
  • %w Skip a whitespace delimited word (see also %c).
  • %y Year. If less than 100, centuryCutoff is used to determine the actual year.
  • %Y Year as found in the input string.
  • %%, %[, %] input the %, [, and ] characters from the input string.
  • [...] square brackets within format specifications indicate optional components; if present, they are used, but they need not be there.

centuryCutoff

integer specifying the changeover year between the twentieth and twenty-first century if two-digit years are read. Values less than centuryCutoffare prefixed by 20 and those greater than or equal to centuryCutoff are prefixed by 19. If you specify 0, all two digit dates are interpreted as years in the twentieth century. Not supported when useFastRead is set to TRUE.

firstRowIsColNames

logical indicating if the first row represents column names for reading text. If firstRowIsColNames is NULL, then column names are auto- detected. The logic for auto-detection is: if the first row contains all values that are interpreted as character and the second row contains at least one value that is interpreted as numeric, then the first row is considered to be column names; otherwise the first row is considered to be the first data row. Not relevant for fixed format data. As for writing, it specifies to write column names as the first row. If firstRowIsColNames is NULL, the default is to write the column names as the first row.

rowsToSniff

number of rows to use in determining column type.

rowsToSkip

integer indicating number of leading rows to ignore. Only supported for useFastRead = TRUE.

defaultReadBufferSize

number of rows to read into a temporary buffer. This value could affect the speed of import.

defaultDecimalColType

Used to specify a column's data type when only decimal values (possibly mixed with missing (NA) values) are encountered upon first read of the data and the column's type information is not specified via colInfo or colClasses. Supported types are "float32" and "numeric", for 32-bit floating point and 64-bit floating point values, respectively.

defaultMissingColType

Used to specify a given column's data type when only missings (NAs) or blanks are encountered upon first read of the data and the column's type information is not specified via colInfo or colClasses. Supported types are "float32", "numeric", and "character" for 32-bit floating point, 64-bit floating point and string values, respectively. Only supported for useFastRead = TRUE.

writePrecision

integer specifying the precision to use when writing numeric data to a file.

stripZeros

logical scalar. If TRUE, if there are only zeros after the decimal point for a numeric, it will be written as an integer to a file.

quotedDelimiters

logical scalar. If TRUE, delimiters within quoted strings will be ignored. This requires a slower parsing process. Only applicable to useFastRead is set to TRUE; delimiters within quotes are always supported when useFastRead is set to FALSE .

isFixedFormat

logical scalar. If TRUE, the input data file is treated as a fixed format file. Fixed format files must have a .sts file or a colInfo argument specifying the start and width of each variable. If FALSE, the input data file is treated as a delimited text file. If NULL, the text file type (fixed or delimited text) is auto-determined.

useFastRead

NULL or logical scalar. If TRUE, the data file is accessed directly by the Microsoft R Services Compute Engine. If FALSE, StatTransfer is used to access the data file. If NULL, the type of text import is auto-determined. useFastRead should be set to FALSE if importing Date or POSIXct data types, if the data set contains the delimiter character inside a quoted string, if the decimalPoint is not ".", if the thousandsSeparator is not ",", if the quoteMark is not "\"", or if combineDelimiters is set to TRUE. useFastRead should be set to TRUE if rowsToSkip or defaultMissingColType are set. If useFastRead is TRUE, by default variables containing the values TRUE and FALSE or T and F will be created as logical variables. useFastRead cannot be set to FALSE if an HDFS file system is being used. If an incompatible setting of useFastRead is detected, a warning will be issued and the value will be changed.

createFileSet

logical value or NULL. Used only when writing. If TRUE, a file folder of text files will be created instead of a single text file. A directory will be created whose name is the same as the text file that would otherwise be created, but with no extension. In the directory, the data will be split across a set of text files (see rowsPerOutFile below for determining how many rows of data will be in each file). If FALSE, a single text file will be created. If NULL, a folder of files will be created if the input data set is a composite XDF file or a folder of text files. This argument is ignored if the text file is fixed format.

rowsPerOutFile

numeric value or NULL. If a directory of text files is being created, and if the compute context is not RxHadoopMR, this will be the number of rows of data put into each file in the directory. When importing is being done on Hadoop using MapReduce, the number of rows per file is determined by the rows assigned to each MapReduce task. If NULL, the rows of data will match the input data.

verbose

integer value. If 0, no additional output is printed. If 1, information on the text type (text or textFast) is printed.

checkVarsToKeep

logical value. If TRUE variable names specified in varsToKeep will be checked against variables in the data set to make sure they exist. An error will be reported if not found. If there are more than 500 variables in the data set, this flag is ignored and no checking is performed.

fileSystem

character string or RxFileSystem object indicating type of file system; "native"or RxNativeFileSystem object can be used for the local operating system, or an RxHdfsFileSystem object for the Hadoop file system.

inputEncoding

character string indicating the encoding used by input text. May be set to either "utf-8" (the default), or "gb18030", a standard Chinese encoding. Not supported when useFastRead is set to TRUE.

writeFactorsAsIndexes

logical. If TRUE, when writing to an RxTextData data source, underlying factor indexes will be written instead of the string representations. Not supported when useFastRead is set to FALSE.

Details

Delimited Data Type Details

Imported POSIXct will have the tzone attribute set to "GMT".

Decimal data in text files can be imported into .xdf files and stored as either 32-bit floats or 64-bit doubles. The default for this is 32-bit floats, which can be changed using rxOptions. If the data type cannot be determined (i.e., only missing values are encountered), the column is imported as 64-bit doubles unless otherwise specified.

If stored in 32-bit floats, they are converted into 64-bit doubles whenever they are brought into R. Because there may be no exact binary representation of a particular decimal number, the resulting double may be (slightly) different from a double created by directly converting a decimal value to a double. Thus exact comparisons of values may result in unexpected behavior. For example, if x is imported from a text file with a decimal value of "1.2" and stored as a float in an .xdf file, the closest decimal representation of the stored value displayed as a double is 1.2000000476837158. So, bringing it into R as a double and comparing with a decimal constant of 1.2, e.g. x == 1.2, will result in FALSE because the decimal constant 1.2 in the code is being converted directly to a double.

To store imported text decimal data as 64-bit doubles in an .xdf file, set the defaultDecimalColType to "numeric". Doing so will increase the size of the .xdf file, since the size of a double is twice that of a float.

Fixed Format Schema Details

The .sts schema for a fixed format data file consists of two required components (FILE and VARIABLES) and one optional component (FIRST LINE), representing the first line of the data file to read.



 FILE  file name and path specification

 FIRST LINE  n       when required

 VARIABLES

        Variable name | variable list | variable range columns  (A)

where (A) is used to tag character columns, else use no tag for numeric columns.

If the data file names and .sts file name are different, the full path must be specified in the FILE component.

See file.show(file.path(rxGetOption("sampleDataDir"), "claims.sts")) for an example fixed format schema file.

If a .sts schema file is used in addition to a colInfo argument, schema file is read first, then the colInfo is used to modify that information (for example, to specify that a variable should be read as a factor).

Encoding Details

Character data in the input file must be encoded as ASCII or UTF-8 in order to be imported correctly. If the data contains UTF-8 multibyte (i.e., non-ASCII) characters, make sure the useFastRead parameter is set to FALSE as the 'fast' version of this object may not handle extended UTF-8 characters correctly.

Value

object of class RxTextData.

Author(s)

Microsoft Corporation Microsoft Technical Support

See Also

RxTextData-class, rxImport, rxNewDataSource.

Examples


 ### Read from a csv file ###
 # Create a csv data source
 claimsCSVFileName <- file.path(rxGetOption("sampleDataDir"), "claims.txt")
 claimsCSVDataSource <- RxTextData(claimsCSVFileName)

 # Specify the location for the new .xdf file
 claimsXdfFileName <- file.path(tempdir(), "importedClaims.xdf")

 # Import the data into the xdf file
 claimsDS <- rxImport(inData = claimsCSVDataSource, 
     outFile = claimsXdfFileName, overwrite = TRUE)

 # Look at file information
 rxGetInfo( claimsDS, getVarInfo = TRUE )

 # Clean-up: delete the new file
 file.remove( claimsXdfFileName)


 ### Read from a fixed format file ###
 # Create a fixed format data source
 claimsFFFileName <- file.path(rxGetOption("sampleDataDir"), "claims.dat")
 claimsFFColInfo <-
   list(rownames = list(start = 1, width = 3),
        age = list(type = "factor", start = 4, width = 5),
        car.age = list(type = "factor", start = 9, width = 3),
        type = list(type = "factor", start = 12, width = 1),
        cost = list(type = "numeric", start = 13, width = 6),
        number = list(type = "integer", start = 19, width = 3))
 claimsFFSource <- RxTextData(claimsFFFileName, colInfo = claimsFFColInfo)

 # Import the data into a data frame
 claimsIn <- rxImport(inData = claimsFFSource)
 rxGetInfo( claimsIn, getVarInfo = TRUE)

 ##############################################################################
 # Import a space delimited text file without variable names
 # Specify names for the data, and use "." for missing values
 # Perform additional transformations when importing
 ##############################################################################

 unitTestDataDir <- rxGetOption("unitTestDataDir")
 gardenDAT <- file.path(unitTestDataDir, "Garden.dat")
 gardenDS <- RxTextData(file=gardenDAT, firstRowIsColNames = FALSE,
     missingValueString=".", 
     colInfo = list(
         list(index = 1, newName = "Name"),
         list(index = 2, newName = "Tomato"),
         list(index = 3, newName = "Zucchini"),
         list(index = 4, newName = "Peas"),
         list(index = 5, newName = "Grapes")) )

 rsrData <- rxImport(inData=gardenDS, 
     transforms = list( 
         Zone = rep(14, .rxNumRows),
         Type = rep("home", .rxNumRows),
         Zucchini = Zucchini * 10,
         Total = Tomato  + Zucchini + Peas + Grapes,
         PerTom = 100*(Tomato/Total))
     )
 rsrData