I have the following function which returns a single value.
function getVolumeHigh_excludeUpBars(period)
{
volume_exclude_up = IIf( ROC(CLOSE,1) < 0, Volume, 0);
SELECTED_BAR = SelectedValue( BarIndex() );
volume_exclude_up[SELECTED_BAR] = Volume[SELECTED_BAR];
volume_High = hhv(volume_exclude_up, period);
return volume_High;
}
I want to convert the above function to return an array instead of a single value. I rewrote the function. Here it is;
function getArray_VolumeHigh_excludeUpBars(period)
{
volume_exclude_up = IIf( ROC(CLOSE,1) < 0, Volume, 0);
for (i=(BAR_COUNT-1);i>=0;i--)
{
volume_exclude_up[i] = Volume[i];
volume_High[i] = hhv(volume_exclude_up, period);
}
return volume_High;
}
The rewritten function is inefficient as it uses for-do loop to assign value individually into the array. Is there a more efficient and elegant way to rewrite the function?
For what you're trying to achieve, this looks like it should be fine
volume_exclude_up = IIf( ROC(CLOSE,1) < 0, Volume, 0);
volume_High = hhv(volume_exclude_up, period);
With
volume_exclude_up[SELECTED_BAR] = Volume[SELECTED_BAR];
and
volume_exclude_up[i] = Volume[i];
you are changing the original volume_exclude_up variable from the conditional to volume.
Either you want volume_exclude_up to equal volume all the time, or equal it conditionally, your code first says equal it conditionally, then changes it's mind and says, equal it all the time. So in effect, decide whether you want
volume_high = hhv(volume_exclude_up, period)
or
volume_high = hhv(v, period)
Related
I'm writing a C extension aggregate function for PostgreSQL , and in C code I would like to know if it is the first time that transition function of the aggregate be called.
For example, I define a aggregate function such as:
CREATE AGGREGATE my_aggregate (text) (
sfunc = my_transfunc,
stype = text,
finalfunc = my_finalfn,
initcond = '');
Then in C code of my_transfunc, how can I know if it is the first time my_transfunc be called ( but not the second, third ... time).
Datum my_transfunc(PG_FUNCTION_ARGS) {
// How to check if the first time function called
if (first_time) { then do something }
else { do some other things }
}
I don't want to use global or static variable here as this made my function is not threaded-safe which violent the requirement for my function.
Generally this is a matter of a proper setting of initcond. Typically you do not need to know whether the function is executed for the first time if only the algorithm is designed properly.
In your case, assuming that the function returns non-empty string, you can check whether the argument is empty (i.e. is equal to initcond). Of course, you can set initcond to a special value instead of an empty string.
Datum my_transfunc(PG_FUNCTION_ARGS) {
text *arg = PG_GETARG_TEXT_PP(0);
int32 arg_size = VARSIZE_ANY_EXHDR(arg);
if (arg_size == 0) { // arg == initcond }
else { // do some other things }
}
This is a tough one, at least for my minimal c skills.
Basically, the user enters a list of prices into an array, and then the desired number of items he wants to purchase, and finally a maximum cost not to exceed.
I need to check how many combinations of the desired number of items are less than or equal to the cost given.
If the problem was a fixed number of items in the combination, say 3, it would be much easier with just three loops selecting each price and adding them to test.
Where I get stumped is the requirement that the user enter any number of items, up to the number of items in the array.
This is what I decided on at first, before realizing that the user could specify combinations of any number, not just three. It was created with help from a similar topic on here, but again it only works if the user specifies he wants 3 items per combination. Otherwise it doesn't work.
// test if any combinations of items can be made
for (one = 0; one < (count-2); one++) // count -2 to account for the two other variables
{
for (two = one + 1; two < (count-1); two++) // count -1 to account for the last variable
{
for (three = two + 1; three < count; three++)
{
total = itemCosts[one] + itemCosts[two] + itemCosts[three];
if (total <= funds)
{
// DEBUG printf("\nMatch found! %d + %d + %d, total: %d.", itemCosts[one], itemCosts[two], itemCosts[three], total);
combos++;
}
}
}
}
As far as I can tell there's no easy way to adapt this to be flexible based on the user's desired number of items per combination.
I would really appreciate any help given.
One trick to flattening nested iterations is to use recursion.
Make a function that takes an array of items that you have selected so far, and the number of items you've picked up to this point. The algorithm should go like this:
If you have picked the number of items equal to your target of N, compute the sum and check it against the limit
If you have not picked enough items, add one more item to your list, and make a recursive call.
To ensure that you do not pick the same item twice, pass the smallest index from which the function may pick. The declaration of the function may look like this:
int count_combinations(
int itemCosts[]
, size_t costCount
, int pickedItems[]
, size_t pickedCount
, size_t pickedTargetCount
, size_t minIndex
, int funds
) {
if (pickedCount == pickedTargetCount) {
// This is the base case. It has the code similar to
// the "if" statement from your code, but the number of items
// is not fixed.
int sum = 0;
for (size_t i = 0 ; i != pickedCount ; i++) {
sum += pickedItems[i];
}
// The following line will return 0 or 1,
// depending on the result of the comparison.
return sum <= funds;
} else {
// This is the recursive case. It is similar to one of your "for"
// loops, but instead of setting "one", "two", or "three"
// it sets pickedItems[0], pickedItems[1], etc.
int res = 0;
for (size_t i = minIndex ; i != costCount ; i++) {
pickedItems[pickedCount] = itemCosts[i];
res += count_combinations(
itemCosts
, costCount
, pickedItems
, pickedCount+1
, pickedTargetCount
, i+1
, funds
);
}
return res;
}
}
You call this function like this:
int itemCosts[C] = {...}; // The costs
int pickedItems[N]; // No need to initialize this array
int res = count_combinations(itemCosts, C, pickedItems, 0, N, 0, funds);
Demo.
This can be done by using a backtracking algorithm. This is equivalent to implementing a list of nested for loops. This can be better understood by trying to see the execution pattern of a sequence of nested for loops.
For example lets say you have, as you presented, a sequence of 3 fors and the code execution has reached the third level (the innermost). After this goes through all its iterations you return to the second level for where you go to the next iteration in which you jump again in third level for. Similarly, when the second level finishes all its iteration you jump back to the first level for which continues with the next iteration in which you jump in the second level and from there in the third.
So, in a given level you try go to the deeper one (if there is one) and if there are no more iterations you go back a level (back track).
Using the backtracking you represent the nested for by an array where each element is an index variable: array[0] is the index for for level 0, and so on.
Here is a sample implementation for your problem:
#define NUMBER_OF_OBJECTS 10
#define FORLOOP_DEPTH 4 // This is equivalent with the number of
// of nested fors and in the problem is
// the number of requested objects
#define FORLOOP_ARRAY_INIT -1 // This is a init value for each "forloop" variable
#define true 1
#define false 0
typedef int bool;
int main(void)
{
int object_prices[NUMBER_OF_OBJECTS];
int forLoopsArray[FORLOOP_DEPTH];
bool isLoopVariableValueUsed[NUMBER_OF_OBJECTS];
int forLoopLevel = 0;
for (int i = 0; i < FORLOOP_DEPTH; i++)
{
forLoopsArray[i] = FORLOOP_ARRAY_INIT;
}
for (int i = 0; i < NUMBER_OF_OBJECTS; i++)
{
isLoopVariableValueUsed[i] = false;
}
forLoopLevel = 0; // Start from level zero
while (forLoopLevel >= 0)
{
bool isOkVal = false;
if (forLoopsArray[forLoopLevel] != FORLOOP_ARRAY_INIT)
{
// We'll mark the loopvariable value from the last iterration unused
// since we'll use a new one (in this iterration)
isLoopVariableValueUsed[forLoopsArray[forLoopLevel]] = false;
}
/* All iterations (in all levels) start basically from zero
* Because of that here I check that the loop variable for this level
* is different than the previous ones or try the next value otherwise
*/
while ( isOkVal == false
&& forLoopsArray[forLoopLevel] < (NUMBER_OF_OBJECTS - 1))
{
forLoopsArray[forLoopLevel]++; // Try a new value
if (loopVariableValueUsed[forLoopsArray[forLoopLevel]] == false)
{
objectUsed[forLoopsArray[forLoopLevel]] = true;
isOkVal = true;
}
}
if (isOkVal == true) // Have we found in this level an different item?
{
if (forLoopLevel == FORLOOP_DEPTH - 1) // Is it the innermost?
{
/* Here is the innermost level where you can test
* if the sum of all selected items is smaller than
* the target
*/
}
else // Nope, go a level deeper
{
forLoopLevel++;
}
}
else // We've run out of values in this level, go back
{
forLoopsArray[forLoopLevel] = FORLOOP_ARRAY_INIT;
forLoopLevel--;
}
}
}
I found a url request having suspicious code to one of my Drupal site. Will someone explain what will be the depth of this code and advise any precautions to be taken. Code:
function (){try{var _0x5757=["/x6C/x65/x6E/x67/x74/x68","/x72/x61/x6E/x64/x6F/x6D","/x66/x6C/x6F/x6F/x72"],_0xa438x1=this[_0x5757[0]],_0xa438x2,_0xa438x3;if(_0xa438x1==0){return};while(--_0xa438x1){_0xa438x2=Math[_0x5757[2]](Math[_0x5757[1]]()*(_0xa438x1 1));_0xa438x3=this[_0xa438x1];this[_0xa438x1]=this[_0xa438x2];this[_0xa438x2]=_0xa438x3;};}catch(e){}finally{return this}}
Site returned page not found error and I observed no issues.
Run this code through a beatifier and you will receive:
function () {
try {
var _0x5757 = ["/x6C/x65/x6E/x67/x74/x68", "/x72/x61/x6E/x64/x6F/x6D", "/x66/x6C/x6F/x6F/x72"],
_0xa438x1 = this[_0x5757[0]],
_0xa438x2, _0xa438x3;
if (_0xa438x1 == 0) {
return
};
while (--_0xa438x1) {
_0xa438x2 = Math[_0x5757[2]](Math[_0x5757[1]]() * (_0xa438x1 1));
_0xa438x3 = this[_0xa438x1];
this[_0xa438x1] = this[_0xa438x2];
this[_0xa438x2] = _0xa438x3;
};
} catch (e) {} finally {
return this
}
}
First, let's rename some variables and decrypt the array of strings in the third line. I've renamed _0x5757 to arr and escaped the hex-chars within the array. That gives you:
var arr = ["length", "random", "floor"],
So here we have a list of functions that will be used shortly. Substitute the strings in and rename the variables and you will receive:
function () {
try {
var arr = ["length", "random", "floor"],
length_func = "length",
rand_number, temp;
if (length_func == 0) {
return
};
while (--length_func) {
rand_number = Math["floor"](Math["random"]() * (length_func 1));
temp = this[length_func];
this[length_func] = this[rand_number];
this[rand_number] = temp;
};
} catch (e) {} finally {
return this
}
}
Notice how there is a syntax error in the script when generating a random number.
* (length_func 1)
with length_func = "length" is not valid JavaScript syntax, so the code is actually not functional. I can still make a guess on what it was supposed to do: If we remove the obfuscation of calling a function by doing Math["floor"] instead of Math.floor() the important lines are
while (--length_func) {
rand_number = Math.floor( Math.random() * ( length 1 ));
temp = this.length_func;
this.length_func = this.rand_number;
this.rand_number = temp;
};
It seems that it tries to compute a random integer using Math.random() and Math.floor(), then swaps the contents of the variables length_func and rand_numerber, all wrapped in a while(--length_func) loop. There's nothing functional here or anything that makes sense. An attempt at an infinte loop hanging the browser maybe? The code is, as it stands, non-functional. It even fails to generate a random number, because Math.floor() will always round-down the inputted float, and Math.rand() will generate a number within 0.0 to 1.0, so nearly always something slightly below 1.0, therefore rand_number = 0 for most of the time. The multiplication with the rand() output with the length_func 1 maybe should have made the number bigger, but the syntax is invalid. When I use my browser's console to execute length, it gives me 0, when I try to do length(1), then length is not a function, the only length that makes sense here is a string-length or array length, but then it would have to explicitly be "someString".length. Hope this helps you.
I have a function called preprocess. It looks like this
function image_utils.preprocess(meanfile, oneD_image_table)
local img_mean = torch.load(meanfile).img_mean:transpose(3,1)
return function()
for t_class, img_path in pairs(oneD_image_table) do
local im3 = image.load(img_path)
local im4 = image.scale(im3,227,227,'bilinear')*25
return im4 - image.scale(img_mean, 227, 227, 'bilinear')
end
end
Here's how I call it:
im_f = image_util.preprocess(meanfile, path_list)
repeat
im=im_f()
batch[count]:copy(im)
count = count + 1
until count == batchSize
This works. However, I would like to be detect when im_f doesn't have any more iterations left and use that to determine when I should stop looping.In other words, something like this:
repeat
im = im_f()
count = count+1
batch[count] = im
until im == nil (or im is some sentinel value that tells me to stop)
However, I have not been able to make this work due to out of range error.
In short, I want to loop until im_f tells me to stop; rather than using a predetermined number to tell me when to stop.
I have a class method that is supposed to take an object and populate a few values in place. This is at the stage of functional demonstration, so the implementation will be better later. right now I just would like this to work.
In the code below, the districtID integer is successfully passed to the if statements. The rgb double array does not make it into the if statement scope. The values set at initialization make it all the way to the districtPoint.color without getting set inside the if statement.
the code below will not compile as is. I would like to know how to get the rgb variable to be visible within the if statement scope.
(note: I tried the naive solution of initializing the variables within the if statement. This clears the error, but doesn't let the new rgb variables out of the if scope)
// This method populates properties
+(void)setContantPropertiesForID:(DistrictPoint *)districtPoint
{
int districtID = [districtPoint.districtID intValue];
double rgb[3] = {0,0,0};
if (districtID == 1) {
districtPoint.title = #"District 1";
rgb = {1.0,0.0,0.0}; // error is expected expression
} else if (districtID == 2) {
districtPoint.title = #"District 1";
rgb = {0.0,1.0,0.0};
} else if (districtID == 3) {
districtPoint.title = #"District 1";
rgb = {0.0,0.0,1.0};
} else {
districtPoint.title = nil;
rgb = {1.0,1.0,1.0}; // error condition
}
districtPoint.color = [UIColor colorWithRed:rgb[0] green:rgb[1] blue:rgb[2] alpha:0.5];
}
This has nothing to do with the if statement. You can use the curly-braces notation to set an array's elements only when initializing (as you do, in fact, earlier in the code).