问题
I have a lot of if, else if statements and I know there has to be a better way to do this but even after searching stackoverflow I'm unsure of how to do so in my particular case.
I am parsing text files (bills) and assigning the name of the service provider to a variable (txtvar.Provider) based on if certain strings appear on the bill.
This is a small sample of what I'm doing (don't laugh, I know it's messy). All in all, There are approximately 300 if, else if's.
if (txtvar.BillText.IndexOf("SWGAS.COM") > -1)
{
txtvar.Provider = "Southwest Gas";
}
else if (txtvar.BillText.IndexOf("georgiapower.com") > -1)
{
txtvar.Provider = "Georgia Power";
}
else if (txtvar.BillText.IndexOf("City of Austin") > -1)
{
txtvar.Provider = "City of Austin";
}
// And so forth for many different strings
I would like to use something like a switch statement to be more efficient and readable but I'm unsure of how I would compare the BillText. I'm looking for something like this but can't figure out how to make it work.
switch (txtvar.BillText)
{
case txtvar.BillText.IndexOf("Southwest Gas") > -1:
txtvar.Provider = "Southwest Gas";
break;
case txtvar.BillText.IndexOf("TexasGas.com") > -1:
txtvar.Provider = "Texas Gas";
break;
case txtvar.BillText.IndexOf("Southern") > -1:
txtvar.Provider = "Southern Power & Gas";
break;
}
I'm definitely open to ideas.
EDIT: To answer the question that is being assumed... Yes, I would need the ability to determine the order in which the values were evaluated. As you can imagine, when parsing for hundreds of slightly different layouts I occasionally run into the issue of not having a distinctly unique indicator as to what service provider the bill belongs to. (Thanks for all the awesome suggestions! I have been out of the office for a few days and will get around to trying them out ASAP)
回答1:
Why not use everything C# has to offer? The following use of anonymous types, collection initializers, implicitly typed variables, and lambda-syntax LINQ is compact, intuitive, and maintains your modified requirement that patterns be evaluated in order:
var providerMap = new[] {
new { Pattern = "SWGAS.COM" , Name = "Southwest Gas" },
new { Pattern = "georgiapower.com", Name = "Georgia Power" },
// More specific first
new { Pattern = "City of Austin" , Name = "City of Austin" },
// Then more general
new { Pattern = "Austin" , Name = "Austin Electric Company" }
// And for everything else:
new { Pattern = String.Empty , Name = "Unknown" }
};
txtVar.Provider = providerMap.First(p => txtVar.BillText.IndexOf(p.Pattern) > -1).Name;
More likely, the pairs of patterns would come from a configurable source, such as:
var providerMap =
System.IO.File.ReadLines(@"C:\some\folder\providers.psv")
.Select(line => line.Split('|'))
.Select(parts => new { Pattern = parts[0], Name = parts[1] }).ToList();
Finally, as @millimoose points out, anonymous types are less useful when passed between methods. In that case we can define a trival Provider class and use object initializers for nearly identical syntax:
class Provider {
public string Pattern { get; set; }
public string Name { get; set; }
}
var providerMap =
System.IO.File.ReadLines(@"C:\some\folder\providers.psv")
.Select(line => line.Split('|'))
.Select(parts => new Provider() { Pattern = parts[0], Name = parts[1] }).ToList();
回答2:
Since you seem to need to search for the key before returning the value a Dictionary is the right way to go, but you will need to loop over it.
// dictionary to hold mappings
Dictionary<string, string> mapping = new Dictionary<string, string>();
// add your mappings here
// loop over the keys
foreach (KeyValuePair<string, string> item in mapping)
{
// return value if key found
if(txtvar.BillText.IndexOf(item.Key) > -1) {
return item.Value;
}
}
EDIT: If you wish to have control over the order in which elemnts are evaluated, use an OrderedDictionary and add the elements in the order in which you want them evaluated.
回答3:
One more using LINQ and Dictionary
var mapping = new Dictionary<string, string>()
{
{ "SWGAS.COM", "Southwest Gas" },
{ "georgiapower.com", "Georgia Power" }
.
.
};
return mapping.Where(pair => txtvar.BillText.IndexOf(pair.Key) > -1)
.Select(pair => pair.Value)
.FirstOrDefault();
If we prefer empty string instead of null when no key matches we can use the ?? operator:
return mapping.Where(pair => txtvar.BillText.IndexOf(pair.Key) > -1)
.Select(pair => pair.Value)
.FirstOrDefault() ?? "";
If we should consider the dictionary contains similar strings we add an order by, alphabetically, shortest key will be first, this will pick 'SCE' before 'SCEC'
return mapping.Where(pair => txtvar.BillText.IndexOf(pair.Key) > -1)
.OrderBy(pair => pair.Key)
.Select(pair => pair.Value)
.FirstOrDefault() ?? "";
回答4:
To avoid the blatant Schlemiel the Painter's approach that looping over all the keys would involve: let's use regular expressions!
// a dictionary that holds which bill text keyword maps to which provider
static Dictionary<string, string> BillTextToProvider = new Dictionary<string, string> {
{"SWGAS.COM", "Southwest Gas"},
{"georgiapower.com", "Georgia Power"}
// ...
};
// a regex that will match any of the keys of this dictionary
// i.e. any of the bill text keywords
static Regex BillTextRegex = new Regex(
string.Join("|", // to alternate between the keywords
from key in BillTextToProvider.Keys // grab the keywords
select Regex.Escape(key))); // escape any special characters in them
/// If any of the bill text keywords is found, return the corresponding provider.
/// Otherwise, return null.
string GetProvider(string billText)
{
var match = BillTextRegex.Match(billText);
if (match.Success)
// the Value of the match will be the found substring
return BillTextToProvider[match.Value];
else return null;
}
// Your original code now reduces to:
var provider = GetProvider(txtvar.BillText);
// the if is be unnecessary if txtvar.Provider should be null in case it can't be
// determined
if (provider != null)
txtvar.Provider = provider;
Making this case-insensitive is a trivial exercise for the reader.
All that said, this does not even pretend to impose an order on which keywords to look for first - it will find the match that's located earliest in the string. (And then the one that occurs first in the RE.) You do however mention that you're searching through largeish texts; if .NET's RE implementation is at all good this should perform considerably better than 200 naive string searches. (By only making one pass through the string, and maybe a little by merging common prefixes in the compiled RE.)
If ordering is important to you, you might want to consider looking for an implementation of a better string search algorithm than .NET uses. (Like a variant of Boyer-Moore.)
回答5:
What you want is a Dictionary:
Dictionary<string, string> mapping = new Dictionary<string, string>();
mapping["SWGAS.COM"] = "Southwest Gas";
mapping["foo"] = "bar";
... as many as you need, maybe read from a file ...
Then just:
return mapping[inputString];
Done.
回答6:
One way of doing it (other answers show very valid options):
void Main()
{
string input = "georgiapower.com";
string output = null;
// an array of string arrays...an array of Tuples would also work,
// or a List<T> with any two-member type, etc.
var search = new []{
new []{ "SWGAS.COM", "Southwest Gas"},
new []{ "georgiapower.com", "Georgia Power"},
new []{ "City of Austin", "City of Austin"}
};
for( int i = 0; i < search.Length; i++ ){
// more complex search logic could go here (e.g. a regex)
if( input.IndexOf( search[i][0] ) > -1 ){
output = search[i][1];
break;
}
}
// (optional) check that a valid result was found.
if( output == null ){
throw new InvalidOperationException( "A match was not found." );
}
// Assign the result, output it, etc.
Console.WriteLine( output );
}
The main thing to take out of this exercise is that creating a giant switch or if/else structure is not the best way to do it.
回答7:
There are several approaches to do this, but for the reason of simplicity, conditional operator may be a choice:
Func<String, bool> contains=x => {
return txtvar.BillText.IndexOf(x)>-1;
};
txtvar.Provider=
contains("SWGAS.COM")?"Southwest Gas":
contains("georgiapower.com")?"Georgia Power":
contains("City of Austin")?"City of Austin":
// more statements go here
// if none of these matched, txtvar.Provider is assigned to itself
txtvar.Provider;
Note the result is according to the more preceded condition which is met, so if txtvar.BillText="City of Austin georgiapower.com"; then the result would be "Georgia Power".
回答8:
you can use dictionary.
Dictionary<string, string> textValue = new Dictionary<string, string>();
foreach (KeyValuePair<string, string> textKey in textValue)
{
if(txtvar.BillText.IndexOf(textKey.Key) > -1)
return textKey.Value;
}
来源：https://stackoverflow.com/questions/18752699/alternative-to-if-else-if