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package dstream
import "fmt"
// xform can be embedded into any transformer object that converts a
// Dstream into another Dstream. It implements the basic behavior
// that is common to all transformers. While xform implements the
// Dstream interface in a trivial way, Types that embed xform can
// provide their own implementation of any of these methods.
//
// In most cases, it will be sufficient to (i) set names properly, and
// (ii) implement Next to set bdata correctly (bdata holds the data
// slices by column). In some cases it may be desirable to implement
// other Dstream methods. Note that due to the way that Go embedding
// works, if a type implements its own, say, Names function, all the
// code below will continue to call the xform Names implementation,
// not the customized Names implementation. For this reason, it is
// usually better to modify the bdata and names members rather than to
// provide new implementations of Get, etc. If Get and other Dstream
// methods need to be implemented by a type, it may be necessary to
// implement all Dstream interface components.
type xform struct {
// The data to be transformed.
source Dstream
// The transformed data, held as references or copies (if
// needed) of the source data.
bdata []interface{}
// List of variable names, used if names for the xform are
// different from the names of its source, otherwise use
// source.Names().
names []string
// Map from variable name to column number
namepos map[string]int
}
func (x *xform) Close() {
}
// setNamePos constructs a map from variable names to their column
// positions.
func (x *xform) setNamePos() {
x.namepos = make(map[string]int)
for k, n := range x.Names() {
x.namepos[n] = k
}
}
func (x *xform) Reset() {
x.source.Reset()
if x.bdata != nil {
truncate(x.bdata)
}
}
func (x *xform) Next() bool {
return x.source.Next()
}
func (x *xform) NumVar() int {
return len(x.Names())
}
func (x *xform) NumObs() int {
return x.source.NumObs()
}
func (x *xform) Names() []string {
// If there is a names, then the xform has modified the names
// so we need to return the modified names, otherwise pass
// through to the source.
if x.names != nil {
return x.names
}
return x.source.Names()
}
func (x *xform) GetPos(j int) interface{} {
// If there is a bdata, then the xform has modified the source
// data so we need to return the modified data, otherwise pass
// through to the source.
if x.bdata != nil {
return x.bdata[j]
}
return x.source.GetPos(j)
}
func (x *xform) Get(na string) interface{} {
if x.namepos == nil {
x.setNamePos()
}
pos, ok := x.namepos[na]
if !ok {
msg := fmt.Sprintf("Variable '%s' not found", na)
panic(msg)
}
return x.GetPos(pos)
}
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