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// Copyright 2016 ALRUX Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package levenshtein
// Params represents a set of parameter values for the various formulas involved
// in the calculation of the Levenshtein string metrics.
type Params struct {
insCost int
subCost int
delCost int
maxCost int
minScore float64
bonusPrefix int
bonusScale float64
bonusThreshold float64
}
var (
defaultParams = NewParams()
)
// NewParams creates a new set of parameters and initializes it with the default values.
func NewParams() *Params {
return &Params{
insCost: 1,
subCost: 1,
delCost: 1,
maxCost: 0,
minScore: 0,
bonusPrefix: 4,
bonusScale: .1,
bonusThreshold: .7,
}
}
// Clone returns a pointer to a copy of the receiver parameter set, or of a new
// default parameter set if the receiver is nil.
func (p *Params) Clone() *Params {
if p == nil {
return NewParams()
}
return &Params{
insCost: p.insCost,
subCost: p.subCost,
delCost: p.delCost,
maxCost: p.maxCost,
minScore: p.minScore,
bonusPrefix: p.bonusPrefix,
bonusScale: p.bonusScale,
bonusThreshold: p.bonusThreshold,
}
}
// InsCost overrides the default value of 1 for the cost of insertion.
// The new value must be zero or positive.
func (p *Params) InsCost(v int) *Params {
if v >= 0 {
p.insCost = v
}
return p
}
// SubCost overrides the default value of 1 for the cost of substitution.
// The new value must be zero or positive.
func (p *Params) SubCost(v int) *Params {
if v >= 0 {
p.subCost = v
}
return p
}
// DelCost overrides the default value of 1 for the cost of deletion.
// The new value must be zero or positive.
func (p *Params) DelCost(v int) *Params {
if v >= 0 {
p.delCost = v
}
return p
}
// MaxCost overrides the default value of 0 (meaning unlimited) for the maximum cost.
// The calculation of Distance() stops when the result is guaranteed to exceed
// this maximum, returning a lower-bound rather than exact value.
// The new value must be zero or positive.
func (p *Params) MaxCost(v int) *Params {
if v >= 0 {
p.maxCost = v
}
return p
}
// MinScore overrides the default value of 0 for the minimum similarity score.
// Scores below this threshold are returned as 0 by Similarity() and Match().
// The new value must be zero or positive. Note that a minimum greater than 1
// can never be satisfied, resulting in a score of 0 for any pair of strings.
func (p *Params) MinScore(v float64) *Params {
if v >= 0 {
p.minScore = v
}
return p
}
// BonusPrefix overrides the default value for the maximum length of
// common prefix to be considered for bonus by Match().
// The new value must be zero or positive.
func (p *Params) BonusPrefix(v int) *Params {
if v >= 0 {
p.bonusPrefix = v
}
return p
}
// BonusScale overrides the default value for the scaling factor used by Match()
// in calculating the bonus.
// The new value must be zero or positive. To guarantee that the similarity score
// remains in the interval 0..1, this scaling factor is not allowed to exceed
// 1 / BonusPrefix.
func (p *Params) BonusScale(v float64) *Params {
if v >= 0 {
p.bonusScale = v
}
// the bonus cannot exceed (1-sim), or the score may become greater than 1.
if float64(p.bonusPrefix)*p.bonusScale > 1 {
p.bonusScale = 1 / float64(p.bonusPrefix)
}
return p
}
// BonusThreshold overrides the default value for the minimum similarity score
// for which Match() can assign a bonus.
// The new value must be zero or positive. Note that a threshold greater than 1
// effectively makes Match() become the equivalent of Similarity().
func (p *Params) BonusThreshold(v float64) *Params {
if v >= 0 {
p.bonusThreshold = v
}
return p
}
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