如何改善多个StringReplace调用？ [英] How to improve multiple StringReplace calls?
问题描述
我从客户那里读取文件，我需要处理读取的数据并删除一些不需要的字符。我的函数可以运行，但是我正在尝试改进FixData函数以提高速度/性能和可维护性。
是否可以用某些东西替换多个StringReplace调用
我找不到MultipleStringReplace或类似的函数。
MCVE：
function FixData（const vStr：string）：string;
var i：integer;
开始
结果：= vStr;
//空字符串
如果Result =＃0，则结果：=’’;
//仅修复换行指示器
如果Result =＃13＃10然后Result：=＃8;
//如果Pos（＃0，Result）>删除'end'/＃0字符
0，然后i的
：= 1到Length（Result）如果Result [i] =＃0，则
执行
，然后
Result [i]：=’′
//＃$ D＃$ A-> ＃8
如果Pos（＃$ D＃$ A，Result）> 0然后
结果：= StringReplace（Result，＃$ D＃$ A，＃8，[rfReplaceAll]）;
//如果Pos（’& #xD;’，结果）>删除& #xD
0，然后
结果：= StringReplace（结果，& #xD;，，[rfReplaceAll]）；
//＃$ A-> ＃8
如果Pos（＃$ A，Result）> 0然后
结果：= StringReplace（Result，＃$ A，＃8，[rfReplaceAll]）;
//如果Pos（chr（34），Result）> 0则$ temp_replacement值
，然后
Result：= StringReplace（Result，chr（34），' \_ /'，[rfReplaceAll]）;
结尾;
过程TForm1.Button1Click（Sender：TObject）;
var vStr，vFixedStr：string;
开始
vStr：='testingmystr： quotest-'+＃0 +'substr& #xD;新行'＃$ A'第二行'＃$ D＃$ A'数据结尾';
vFixedStr：= FixData（vStr）;
结尾;
我想，您必须将字符串拆分为一组字符串（非定界符和定界符（模式）），然后替换数组中的项，然后再次将其组合回去。并转到较短的代码（针对pattern-inside-pattern进行安全检查），那么另一轮操作将是进行一个字符到一个字符的替换（因为它们可以就地完成，并且不需要内存复制）
双重复制，搜索比例为O（Length（input）* Cou nt（Delimiters））。
类似于此伪代码草稿（未实现到最后一个点，只是为了让您有个主意）：
由于您的模式很短，我认为可以进行线性搜索，否则需要更优化但更复杂的算法： https://en.wikipedia.org/wiki/String_searching_algorithm#Algorithms_using_a_finite_set_of_patterns
Type TReplaceItem = record（match，subst：string;位置：整数）；
var匹配项：TReplaceItem数组；
SetLength（matches，3）;
match [0] .match：=‘& #xD;’; //最长的第一；
matchs [0] .subst：=’’;
match [1] .match：=＃$ D＃$ A; //最长的第一；
matchs [1] .subst：=＃8;
matchs [2] .match：=＃34; //最长的第一；
匹配[2] .subst：=‘\_ /’;
sb：= TStringBuilder.Create（2 * Length（InputString））;
//或TList< String>或Jedi CodeLib的iJclStringList或TStringList ...取决于性能和首选项
//容量参数用于-预热，预分配内存，通常足够
试试
NextLetterToParse：= 1;
for I：=低（匹配）到高（匹配）执行
match [I] .position：= PosEx（matches [I] .match，InputString，NextLetterToParse）;
True时开始
ClosestMatchIdx：= -1;
ClosestMatchPos：= {最小匹配[???]。位置> = NextLetterToParse};
ClosestMatchIdx：= {如果最小，则等于[索引]-高于最小值[???]或保持为-1}
如果ClosestMatchIdx< 0 {我们没有更多的匹配项}，然后开始
//转储所有剩余的尚未解析的其余
SB.Append（Copy（InputString，NextLetterToParse，Length（InputString））;;
//退出stage1：拆分循环
中断；
结束；
//转储not-的next-next-delimiter部分输入
的解析后尾// //可能没有-如果ClosestMatchPos> NextLetterToParse然后
SB.Append（Copy（InputString，NextLetterToParse，ClosestMatchPos- NextLetterToParse）;
//转储分隔符模式
SB.Append（match [ClosestMatchIdx] .Subst）;
ShiftLength：=（ClosestMatchPos -NextLetterToParse）+ Length（matches [ClosestMatchIdx] .Match）;
//现在已经丢弃了多余的部分
Inc（NextLetterToParse，ShiftLength）;
对于我：=低（匹配）到高（匹配）做
如果匹配[I] .position<然后NextLetterToParse
match [I] .position：= PosEx（matches [I] .match，InputString，NextLetterToParse）;
//为每个受影响的定界符更新下一个最近的位置，
//那些影响太远而不会受到影响的位置（通常是所有
//但正在被丢弃的那个）重新扫描
结束； //下一阶段的循环迭代
现在我们有一个容器/数组/列表/包含非匹配的块和替换的模式。除了就地一字符替换。是时候合并并进行最后一次扫描了。
Stage2String：= SB.ToString（）;
最终
SB.Destroy;
结尾； I的
：= 1到Length（Stage2String）执行
情况
的Stage2String [I]＃0：Stage2String [I]：=＃32;
＃10，＃13：Stage2String [I]：=＃8;
// BTW-有时无需尾随即可满足^ M =＃13 =＃$ D ^ J =＃10 =＃$ A
// //这是以前使用的行结束符Macintosh文本文件
else； //不执行任何操作，使其保持原样，即
结尾；
结果：= Stage2String;
I read files from customers and I need to process the read data and remove some unneeded characters. My function works, but I'm trying to improve the FixData function to improve speed/performance and maintainability.
Is it possible to replace multiple StringReplace calls with something that will only loop through data once and replace with whatever it needs to?
I can't find MultipleStringReplace or similar function.
MCVE:
function FixData(const vStr:string):string;
var i:integer;
begin
Result:=vStr;
// empty string
if Result = #0 then Result := '';
// fix just New line indicator
if Result = #13#10 then Result := #8;
// remove 'end'/#0 characters
if Pos(#0, Result) > 0 then
for i := 1 to Length(Result) do
if Result[i] = #0 then
Result[i] := ' ';
// #$D#$A -> #8
if Pos(#$D#$A, Result) > 0 then
Result := StringReplace(Result, #$D#$A, #8, [rfReplaceAll]);
// remove 
if Pos('
', Result) > 0 then
Result := StringReplace(Result, '
', '', [rfReplaceAll]);
// #$A -> #8
if Pos(#$A, Result) > 0 then
Result := StringReplace(Result, #$A, #8, [rfReplaceAll]);
// replace " with temp_replacement value
if Pos(chr(34), Result) > 0 then
Result := StringReplace(Result, chr(34), '\_/', [rfReplaceAll]);
end;
procedure TForm1.Button1Click(Sender: TObject);
var vStr,vFixedStr:string;
begin
vStr:='testingmystr:"quotest" - '+#0+' substr 
 new line '#$A' 2nd line '#$D#$A' end of data';
vFixedStr:=FixData(vStr);
end;
I guess, you have to split your string into a set of strings ( non-delimiters and delimiters(patterns) ) and then replace items in the array and then combine them back yet again. You would start with longer patterns and go to shorter ones (safety check against pattern-inside-pattern), then an extra run would be to make one-char-to-one-char substitutions (as they can be done in-place and would not require memory copying).
Double copy, and search scaling as O(Length(input)*Count(Delimiters)).
Something like this pseudocode draft (not implemented to the last dot, just for you to have the idea):
Since your patterns are short I think linear search would be okay, otherwise more optimized but complex algorithms would be needed: https://en.wikipedia.org/wiki/String_searching_algorithm#Algorithms_using_a_finite_set_of_patterns
Hash it to smaller functions as you see fit for ease of understanding/maintenance.
Type TReplaceItem = record (match, subst: string; position: integer);
var matches: array of TReplaceItem;
SetLength(matches, 3);
matches[0].match := '
'; // most long first;
matches[0].subst := '';
matches[1].match := #$D#$A; // most long first;
matches[1].subst := #8;
matches[2].match := #34; // most long first;
matches[2].subst := '\_/';
sb := TStringBuilder.Create( 2*Length(InputString) );
// or TList<String>, or iJclStringList of Jedi CodeLib, or TStringList... depending on performance and preferences
// Capacity parameter is for - warming up, pre-allocating memory that is "usually enough"
try
NextLetterToParse := 1;
for I := Low(matches) to high(matches) do
matches[I].position := PosEx(matches[I].match, InputString, NextLetterToParse );
While True do begin
ClosestMatchIdx := -1;
ClosestMatchPos := { minimal match[???].Position that is >= NextLetterToParse };
ClosestMatchIdx := {index - that very [???] above - of the minimum, IF ANY, or remains -1}
if ClosestMatchIdx < 0 {we have no more matches} then begin
//dump ALL the remaining not-yet-parsed rest
SB.Append( Copy( InputString, NextLetterToParse , Length(InputString));
// exit stage1: splitting loop
break;
end;
// dumping the before-any-next-delimiter part of not-parsed-yet tail of the input
// there may be none - delimiters could go one after another
if ClosestMatchPos > NextLetterToParse then
SB.Append( Copy( InputString, NextLetterToParse, ClosestMatchPos-NextLetterToParse);
// dumping the instead-of-delimiter pattern
SB.Append( matches[ ClosestMatchIdx ].Subst );
ShiftLength := (ClosestMatchPos - NextLetterToParse) + Length(matches[ ClosestMatchIdx ].Match);
// that extra part got already dumped now
Inc( NextLetterToParse, ShiftLength);
for I := Low(matches) to high(matches) do
if matches[I].position < NextLetterToParse then
matches[I].position := PosEx(matches[I].match, InputString, NextLetterToParse );
// updating next closest positions for every affected delimiter,
// those that were a bit too far to be affected ( usually all
// but the one being dumped) need not to be re-scanned
end; // next stage 1 loop iteration
Now we have a container/array/list/anything comprised of non-matched chunks and replaced patterns. Except for in-place one-char replacement. Time to merge and do one last scan.
Stage2String := SB.ToString();
finally
SB.Destroy;
end;
for I := 1 to Length( Stage2String ) do
case Stage2String[I] of
#0: Stage2String[I] := #32;
#10, #13: Stage2String[I] := #8;
// BTW - ^M=#13=#$D sometimes can be met without trailing ^J=#10=#$A
// that was the end-of-line char used in old Macintosh text files
else ; // do nothing, let it stay as is
end;
Result := Stage2String;
这篇关于如何改善多个StringReplace调用？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
