Transformations

Introduction

Transformation is the process of modifying the data (for example, dividing all of the data values in a field by 10) or deriving new data for analysis (for example, summing the data in two fields). Sometimes it will be easier to use a spreadsheet to calculate derived variables than to modify variables using ASReml transformations.

Note that in ASReml
  • alpha and integer fields are converted to numbers before transformations are applied,
  • transformations may be applied to any data field since all data fields are stored as real numbers, but it may not be sensible to change factor level codes,
  • all fields in a record are read before transformations are performed,
  • transformations are performed in the order of appearance.

    • Syntax

    Transformations have one of six forms, namely
    Forms Function Example
    !o to perform an operation on the current field !ABS
    to take absolute values,
    !o v to perform an operation involving an argument on the current field, !+3
    to add 3 to all elements in the field,
    !oVn to perform an operation o on the current field using the data in another field ( v ) !-V2 to subtract field 2 from the current field.
    !Vt to change the field modified by subsequent transformations, !V12
    changes focus to variable 12
    !Vt=c to change all of the data in a target field to a given value, !V12=1.
    !Vt=Vn copy field n to field t; special case is !Vt=V0 instructing ASReml to put the record number into the target !V12=V3
    In these definitions, V is the literal captital V character. The combination Vn can be replaced by the LABEL of the field if the field is already labelled.

    Rules

  • ! flags the presence of the transformation
  • o is the operator or function name,
  • v is the argument required by the transformation,
  • V is a literal character and is followed by the number t (target) or n (argument) of the data field; the data field is used or modified depending on the context,
  • Vt or Vn may be replaced by the name of the field if the field is already named.
  • in the first three forms the operation is performed on
    • the current field; this will be the field associated with the label unless this field has been reset by specifying a new target in a preceding transformation,
  • the fourth form changes the focus
    • for subsequent transformations to the field target,
  • in the last two forms the operation
    • is performed on the target field which is modified as a consequence, for example, to create a copy of field 11, which is an existing data field, we would use 
     !V22=V11
    which copies field 11 into field 22; if field 22 does not exist in the data it is created; note that subsequent transformations on the line will also apply to the target ,
  • ASReml expects to read values for each variable from the data file unless the variable
    • and all subsequent ones are created using != . The number of variables read can be explicitly set using the !READ qualifier

    Transformation functions

  • arithmetic operators = + - * / ^ == <= >= <>
  • Algebraic operators ABS ARCSIN SIN COS EXP MIN MAX MOD
  • genetic marker operators MMAP DOM
  • date operators Jddm Jmmd Jyyd Jddy
  • Drop records D
  • missing value operators M NA
  • substitution operators SEQ SET SUB REPLACE RESCALE
  • distribution operators SEED NORMAL UNIFORM

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