so the title essentially says it all. I am writing a symbol table in c++ for a compiler project I am working on, and all is going well except for looking up identifiers in the table.
So this is how I store into the table (pseudo like):
vector<symbolTable*>* symbolStack = new symbolTable();
//where a symbolStack is a vector of unordered_maps (symbolTables),
//each iteration in vector referencing a new block of code.
string* check = new string(root->children[0]->lexicode->c_str());
symbol* sym = new symbol();
...... //setting sym info
symbol_entry pair = make_pair(check, test)
//the unordered_map has keys of (string*, symbol*)
symbolStack[tableNumber]->insert(pair);
I am pretty solid that this works, as I have tested printing the size/infos from the map and it all seems to be storing as expect. Here is where the problem is happening for me (this takes place in a different function later):
for(int i = 0; i =< tableNumber;i++){
auto finder = symbolStack[i]->find(checkS) //checkS == check from above
if(finder == symbolStack[i]->end()) cout<<not found;
else cout<<we did it!!!!
My else is never reached. However, if I do this assuming the string*->c_str() == "test":
cout<<string->c_str(); // prints out "test"
cout<<finder->second->c_str() //prints out "test".
So the question. Why is it finding the key, and knowing it found the key, but at the same time returning that is has reached the end of the symbol stack without finding it? I have been trying to figure this out for a good 4 days solid now. Is it that my pointers are somehow off? Any insight is appreciated greatly.
So somewhat answer to my own question.
First I will say this: I have concluded the comparison with find() or similar methods do not work because for some reason the pointers are not matching up. I have no clue why this is still, or what I am doing wrong.
What I did to solve my issue and complete my code is this:
for(int k = 0; k<= tableNumber; k++){
unordered_map<string*,symbol*>::iterator it;
for(it = symbolStack[k]->begin(); it != symbolStack[k]->end(); it++)
{
string a = targetString->c_str();
string b = it->first->c_str();
if(a.compare(b) == 0) cout<<"You have found the match! \n";
}
}
}
So this answers how to get it working pragmatically if somebody else is in a similar ship, however not really answers why my other attempt failed other than noticing the pointer values were different.
In symbolTable you store pointers to strings as keys, not strings themselves. Therefore unordered_map compares pointers, not strings, and cannot find matching items. When you reconstruct the key string (as in your answer, using string b = it->first->c_str()), the comparison on strings works again. So, either you need to store string instead of string * in symbolTable, or you need to provide your own comparison function that will compare keys of type string *.
Related
Im Vladimir Grygov and I have very serious problem.
In our work we now work on really hard algorithm, which using limits to cout the specific result.
Alghoritm is veary heavy and after two months of work we found really serious problem. Our team of analytics told me to solve this problem.
For the first I tell you the problem, which must be solve by limits:
We have veary much datas in the database. Ec INT_MAX.
For each this data we must sort them by the alghoritm to two groups and one must have red color interpretation and second must be blue.
The algorithm counts with ID field, which is some AUTO_INCREMENT value. For this value we check, if this value is eequal to 1. If yeas, this is red color data. If it is zero, this is blue data. If it is more. Then one, you must substract number 2 and check again.
We choose after big brainstorming method by for loop, but this was really slow for bigger number. So we wanted to remove cycle, and my colegue told me use recursion.
I did so. But... after implementation I had got unknown error for big integers and for example long long int and after him was wrote that: "Stack Overflow Exception"
From this I decided to write here, because IDE told me name of this page, so I think that here may be Answer.
Thank You so much. All of you.
After your comment I think I can solve it:
public bool isRed(long long val) {
if (val==1)
{return true; }
else if (val==0)
{ return false; }
else { return isRed(val - 2); }
}
Any halfway decent value for val will easily break this. There is just no way this could have worked with recursion. No CPU will support a stacktrace close to half long.MaxInt!
However there are some general issues with your code:
Right now this is the most needlesly complex "is the number even" check ever. Most people use Modulo to figure that out. if(val%2 == 0) return false; else return true;
the type long long seems off. Did you repeat the type? Did you mean to use BigInteger?
If the value you substract by is not static and it is not solveable via modulo, then there is no reason not to use a loop here.
public bool isRed (long long val){
for(;val >= 0; val = val -2){
if(value == 0)
return false;
}
return true;
}
I'm wanting to remove all of a possibly duplicated value in an array. At the moment I'm using the remove(x:T):Bool function in a while loop, but I'm wondering about the expression part.
I've started by using:
function removeAll(array:Array<String>, element:String):Void
while (array.remove(element)) {}
but I'm wondering if any of these lines would be more efficient:
while (array.remove(element)) continue;
while (array.remove(element)) true;
while (array.remove(element)) 0;
or if it makes any kind of difference.
I'm guessing that using continue is less efficient because it actually has to do something, true and 0 are slightly more efficient, but still do something, and {} would probably be most efficient.
Does anyone have any background information on this?
While other suggested filter, it will create a new instance of list/array which may cause your other code to lose reference.
If you loop array.remove, it is going to loop through all the elements in the front of the array every time, which is not so performant.
IMO a better approach is to use a reverse while loop:
var i = array.length;
while(--i >= 0)
if(array[i] == element) array.splice(i, 1);
It doesn't make any difference. In fact, there's not even any difference in the generated code for the {}, 0 and false cases: they all end up generating {}, at least on the JS target.
However, you could run into issues if you have a large array with many duplicates: in that case, remove() would be called many times, and it has to iterate over the array each time (until it finds a match, that is). In that case, it's probably more efficient to use filter():
function removeAll(array:Array<String>, element:String):Array<String>
return array.filter(function(e) return e != element);
Personally, I also find this to be a bit more elegant than your while-loop with an empty body. But again, it depends on the use case: this does create a new array, and thus causes an allocation. Usually, that's not worth worrying about, but if you for instance do it in the update loop of a game, you might want to avoid it.
In terms of the expression part of the while loop, it seems that it's just set to empty brases ({}) when compiled so it doesn't really matter what you do.
In terms of performance, a much better solution is the Method 2 from the following:
class Test
{
static function main()
{
var thing:Array<String> = new Array<String>();
for (index in 0...1000)
{
thing.push("0");
thing.push("1");
}
var copy1 = thing.copy();
var copy2 = thing.copy();
trace("epoch");
while (copy1.remove("0")) {}
trace("check");
// Method 2.
copy2 = [
for (item in Lambda.filter(copy2, function(v)
{return v != "0";}))
item
];
trace("check");
}
}
which can be seen [here](https://try.haxe.org/#D0468"Try Haxe example."). For 200,000 one-character elements in an Array<String>, Method 2 takes 0.017s while Method 1 takes 44.544s.
For large arrays it will be faster to use a temporary array and then assign that back after populating ( method3 in try )?
OR
If you don't want to use a temp you can assign back and splice ( method4 in try )?
https://try.haxe.org/#5f80c
Both are more verbose codewise as I setup vars, but on mac seems faster at runtime, summary of my method3 approach:
while( i < l ) { if( ( s = copy[ i++ ] ) != '0' ) arr[ j++ ] = s;
copy = arr;
am I missing something obvious against these approaches?
Most Frequent Character
Design a program that prompts the user to enter a string, and displays the character that appears most frequently in the string.
It is a homework question, but my teacher wasn't helpful and its driving me crazy i can't figure this out.
Thank You in advance.
This is what i have so far!
Declare String str
Declare Integer maxChar
Declare Integer index
Set maxChar = 0
Display “Enter anything you want.”
Input str
For index = 0 To length(str) – 1
If str[index] =
And now im stuck. I dont think its right and i dont know where to go with it!
It seems to me that the way you want to do it is:
"Go through every character in the string and remember the character we've seen most times".
However, that won't work. If we only remember the count for a single character, like "the character we've seen most times is 'a' with 5 occurrences", we can't know if perhaps the character in the 2nd place doesn't jump ahead.
So, what you have to do is this:
Go through every character of the string.
For every character, increase the occurrence count for that character. Yes, you have to save this count for every single character you encounter. Simple variables like string or int are not going to be enough here.
When you're done, you're left with a bunch of data looking like "a"=5, "b"=2, "e"=7,... you have to go though that and find the highest number (I'm sure you can find examples for finding the highest number in a sequence), then return the letter which this corresponds to.
Not a complete answer, I know, but that's all I'm going to say.
If you're stuck, I suggest getting a pen and a piece of paper and trying to calculate it manually. Try to think - how would you do it without a computer? If your answer is "look and see", what if the text is 10 pages? I know it can be pretty confusing, but the point of all this is to get you used to a different way of thinking. If you figure this one out, the next time will be easier because the basic principles are always the same.
This is the code I have created to count all occurences in a string.
String abc = "aabcabccc";
char[] x = abc.toCharArray();
String _array = "";
for(int i = 0; i < x.length; i++) //copy distinct data to a new string
{
if(_array.indexOf(x[i]) == -1)
_array = _array+x[i];
}
char[] y = _array.toCharArray();
int[] count1 = new int[_array.length()];
for(int j = 0; j<x.length;j++) //count occurences
{
count1[new String(String.valueOf(y)).indexOf(x[j])]++;
}
for(int i = 0; i<y.length;i++) //display
{
System.out.println(y[i] + " = " + count1[i]);
}
I am looking if there is an "easy" or simple way to make an array of something, Lets say Icecreams.. this would be a class of icecream with various Attributes (ID, flavour, Size, scoops), i would like to run an array that gathers every ice cream ordered and then searches through this list for any duplicate values (2+ same size)
First idea i had was a for loop that creates the array than grabs the ice cream ID for the first instance, and checks its "flavour" against the array, if no duplicate is found the ID is increased by 1 (ID++) and then that Ice creams flavour is ran in the array, if a match is found i would set a Boolean to true.
Every approach i seem to take appears to be rather long winded and i haven't got one working as of yet. hoping some fresh/more experienced eyes would help on this.
In answer to below;
The XML would hold something like below
<iceCream id=1>
<flavour>chocolate</flavour>
<scoops>5</scoops>
</iceCream>
<iceCream id=2>
<flavour>banana</flavour>
<scoops>2</scoops>
</iceCream>
I would want to use drools (probably an array list?) to gather each icecream tag and allow me to check if any of the icecreams have the same flavour and output something (set a boolean to true) if a match is found, My understand was to make an array then run each icecream though the array by using its ID to identify it and inside each loop do ID +1 (int ID = 1) then in the lopp ID++. Aswell as search through the flavour childtag.
int ID = 0;
boolean match = false;
ArrayList iceCreams = new ArrayList($cont.getIceCreams());
for(iceCream $Flavour: (ArrayList<iceCream>)iceCreams)
{
ID++
if($Flavour.getFlavour().equals(icecream with id of (ID variable).getFlavour)
{
match = true;
}
}
if(match)
{etc etc etc}
Something along these lines if this helps?
1) If you have control over the first array creation, why dont you make sure that while insertion, you insert only the icecreams that are unique. So, while you are inserting into the array say ID=1, first iterate through the array and check if there is an icecream in the array with ID as 1, if not you put this into the array and do other stuff.
2) Searching part: now while inserting, make sure that you are doing so based on the ascending oder of IDs, so you can perform binary search for the same.
Note: I dont know drools, i have just posted a logic as per my understanding of the problem.
I don't know drools either, but I'll post the some pseudo code for what I think you are trying to accomplish:
for(i = 0; i < len(ice_cream_array); i++)
{
for(j = (i + 1); j < len(ice_cream_array); j++)
{
if (ice_cream_array[i] == ice_cream_array[j])
break from inner loop
else
there is no match
}
}
You may also want to look up bubble sorts and binary searches.
This is similar to a question I asked before, but is slightly different:
So I have a very large structure array in matlab. Suppose, for argument's sake, to simplify the situation, suppose I have something like:
structure(1).name, structure(2).name, structure(3).name structure(1).returns, structure(2).returns, structure(3).returns (in my real program I have 647 structures)
Suppose further that structure(i).returns is a vector (very large vector, approximately 2,000,000 entries) and that a condition comes along where I want to delete the jth entry from structure(i).returns for all i. How do you do this? or rather, how do you do this reasonably fast? I have tried some things, but they are all insanely slow (I will show them in a second) so I was wondering if the community knew of faster ways to do this.
I have parsed my data two different ways; the first way had everything saved as cell arrays, but because things hadn't been working well for me I parsed the data again and placed everything as vectors.
What I'm actually doing is trying to delete NaN data, as well as all data in the same corresponding row of my data file, and then doing the very same thing after applying the Hampel filter. The relevant part of my code in this attempt is:
for i=numStock+1:-1:1
for j=length(stock(i).return):-1:1
if(isnan(stock(i).return(j)))
for k=numStock+1:-1:1
stock(k).return(j) = [];
end
end
end
stock(i).return = sort(stock(i).return);
stock(i).returnLength = length(stock(i).return);
stock(i).medianReturn = median(stock(i).return);
stock(i).madReturn = mad(stock(i).return,1);
end;
for i=numStock:-1:1
for j = length(stock(i+1).volume):-1:1
if(isnan(stock(i+1).volume(j)))
for k=numStock:-1:1
stock(k+1).volume(j) = [];
end
end
end
stock(i+1).volume = sort(stock(i+1).volume);
stock(i+1).volumeLength = length(stock(i+1).volume);
stock(i+1).medianVolume = median(stock(i+1).volume);
stock(i+1).madVolume = mad(stock(i+1).volume,1);
end;
for i=numStock+1:-1:1
for j=stock(i).returnLength:-1:1
if (abs(stock(i).return(j) - stock(i).medianReturn) > 3*stock(i).madReturn)
for k=numStock+1:-1:1
stock(k).return(j) = [];
end
end;
end;
end;
for i=numStock:-1:1
for j=stock(i+1).volumeLength:-1:1
if (abs(stock(i+1).volume(j) - stock(i+1).medianVolume) > 3*stock(i+1).madVolume)
for k=numStock:-1:1
stock(k+1).volume(j) = [];
end
end;
end;
end;
However, this returns an error:
"Matrix index is out of range for deletion.
Error in Failure (line 110)
stock(k).return(j) = [];"
So instead I tried by parsing everything in as vectors. Then I decided to try and delete the appropriate entries in the vectors prior to building the structure array. This isn't returning an error, but it is very slow:
%% Delete bad data, Hampel Filter
% Delete bad entries
id=strcmp(returns,'');
returns(id)=[];
volume(id)=[];
date(id)=[];
ticker(id)=[];
name(id)=[];
permno(id)=[];
sp500(id) = [];
id=strcmp(returns,'C');
returns(id)=[];
volume(id)=[];
date(id)=[];
ticker(id)=[];
name(id)=[];
permno(id)=[];
sp500(id) = [];
% Convert returns from string to double
returns=cellfun(#str2double,returns);
sp500=cellfun(#str2double,sp500);
% Delete all data for which a return is not a number
nanid=isnan(returns);
returns(nanid)=[];
volume(nanid)=[];
date(nanid)=[];
ticker(nanid)=[];
name(nanid)=[];
permno(nanid)=[];
% Delete all data for which a volume is not a number
nanid=isnan(volume);
returns(nanid)=[];
volume(nanid)=[];
date(nanid)=[];
ticker(nanid)=[];
name(nanid)=[];
permno(nanid)=[];
% Apply the Hampel filter, and delete all data corresponding to
% observations deleted by the filter.
medianReturn = median(returns);
madReturn = mad(returns,1);
for i=length(returns):-1:1
if (abs(returns(i) - medianReturn) > 3*madReturn)
returns(i) = [];
volume(i)=[];
date(i)=[];
ticker(i)=[];
name(i)=[];
permno(i)=[];
end;
end
medianVolume = median(volume);
madVolume = mad(volume,1);
for i=length(volume):-1:1
if (abs(volume(i) - medianVolume) > 3*madVolume)
returns(i) = [];
volume(i)=[];
date(i)=[];
ticker(i)=[];
name(i)=[];
permno(i)=[];
end;
end
As I said, this is very slow, probably because I'm using a for loop on a very large data set; however, I'm not sure how else one would do this. Sorry for the gigantic post, but does anyone have a suggestion as to how I might go about doing what I'm asking in a reasonable way?
EDIT: I should add that getting the vector method to work is probably preferable, since my aim is to put all of the return vectors into a matrix and get all of the volume vectors into a matrix and perform PCA on them, and I'm not sure how I would do that using cell arrays (or even if princomp would work on cell arrays).
EDIT2: I have altered the code to match your suggestion (although I did decide to give up speed and keep with the for-loops to keep with the structure array, since reparsing this data will be way worse time-wise). The new code snipet is:
stock_return = zeros(numStock+1,length(stock(1).return));
for i=1:numStock+1
for j=1:length(stock(i).return)
stock_return(i,j) = stock(i).return(j);
end
end
stock_return = stock_return(~any(isnan(stock_return)), : );
This returns an Index exceeds matrix dimensions error, and I'm not sure why. Any suggestions?
I could not find a convenient way to handle structures, therefore I would restructure the code so that instead of structures it uses just arrays.
For example instead of stock(i).return(j) I would do stock_returns(i,j).
I show you on a part of your code how to get rid of for-loops.
Say we deal with this code:
for j=length(stock(i).return):-1:1
if(isnan(stock(i).return(j)))
for k=numStock+1:-1:1
stock(k).return(j) = [];
end
end
end
Now, the deletion of columns with any NaN data goes like this:
stock_return = stock_return(:, ~any(isnan(stock_return)) );
As for the absolute difference from medianVolume, you can write a similar code:
% stock_return_length is a scalar
% stock_median_return is a column vector (eg. [1;2;3])
% stock_mad_return is also a column vector.
median_return = repmat(stock_median_return, stock_return_length, 1);
is_bad = abs(stock_return - median_return) > 3.* stock_mad_return;
stock_return = stock_return(:, ~any(is_bad));
Using a scalar for stock_return_length means of course that the return lengths are the same, but you implicitly assume it in your original code anyway.
The important point in my answer is using any. Logical indexing is not sufficient in itself, since in your original code you delete all the values if any of them is bad.
Reference to any: http://www.mathworks.co.uk/help/matlab/ref/any.html.
If you want to preserve the original structure, so you stick to stock(i).return, you can speed-up your code using essentially the same scheme but you can only get rid of one less for-loop, meaning that your program will be substantially slower.