I have a location object with latitude and longitude attributes and I want to query the database for objects within a specific distance from a current latitude / longitude location.
I read about the 'geocoder' gem which seems to be able to do what I'm looking for, but in order to add the obj.near functionality I need to add geocoding to the object.
I don't need geocoding or reverse geocoding at all, just distance queries by coordinates.
can I add the .near functionality to an object with 'geocoder' without adding any geocoding functionality ? is there another or a better way to do what I want ?
Why don't you look at the geocoder source? It's on github. I think the class you are looking for is stores/active_record.rb
Obviously you won't be getting the extensibility or other benefits of using a library but this will give you the code you need.
Edit: This will give you a UDF in mysql that will calculate the distance
DROP FUNCTION IF EXISTS calculateDistance;
delimiter |
CREATE FUNCTION calculateDistance (originLatitude FLOAT, originLongitude FLOAT, targetLatitude FLOAT, targetLongitude FLOAT)
returns FLOAT
deterministic
BEGIN
DECLARE radianConversion FLOAT;
DECLARE interim FLOAT;
DECLARE earthRadius FLOAT;
SET radianConversion = 180 / pi() ;/*57.2957795130823;*/
SET interim = SIN(originLatitude/radianConversion) * SIN(targetLatitude/radianConversion) + COS(originLatitude/radianConversion) * COS(targetLatitude/radianConversion) * COS(targetLongitude/radianConversion - originLongitude/radianConversion);
IF interim > 1 THEN
SET interim = 1;
ELSEIF interim < -1 THEN
SET interim = -1;
END IF;
SET earthRadius = 6371.0072;
RETURN earthRadius * ACOS(interim);
END|
delimiter ;
select calculateDistance(43.6667,-79.4167,45.5000,-73.5833);
Then you just need to pass the correct values from a method on your class to get this to fire off. Obviously this won't work on Sqlite
There is a RailsCast about Geocoder, from what I've seen you need to add latitude and longitude to your model and gecoder will work.
Related
I am trying to create a EA in mql4, but in OrderSend function, when i use some value instead of zero it show ordersend error 130. Please help to solve this problem
Code line is
int order = OrderSend("XAUUSD",OP_SELL,0.01,Bid,3,Bid+20*0.01,tp,"",0,0,Red);
error number 130 means Invalid stops.
so that means there is a problem with the stops you set with the ordersend function.
I suggest you set it like that:
int order = OrderSend("XAUUSD",OP_SELL,0.01,Bid,3,Bid+20*Point,tp,"",0,0,Red);
so you could use Point instead of hard coding it.
and to check what is the error number means. I think you could refer to: https://book.mql4.com/appendix/errors
You should know that there exists a minimum Stop Loss Size (mSLS) given in pips. "mSLS" changes with the currency and broker. So, you need to put in the OnInit() procedure of your EA a variable to get it:
int mSLS = MarketInfo(symbol,MODE_STOPLEVEL);
The distance (in pips) from your Order Open Price (OOP) and the Stop-Loss Price (SLP) can not be smaller than mSLS value.
I will try to explain a general algorithm I use for opening orders in my EAs, and then apply the constrain on Stop-Loss level (at step 3):
Step 1. I introduce a flag (f) for the type of operation I will open, being:
f = 1 for Buy, and
f = -1 for Sell
You know that there are mql4 constants OP_SELL=1 and OP_BUY=0 (https://docs.mql4.com/constants/tradingconstants/orderproperties).
Once I have defined f, I set my operation type variable to
int OP_TYPE = int(0.5((1+f)*OP_BUY+(1-f)*OP_SELL));
that takes value OP_TYPE=OP_BUY when f=1, while OP_TYPE=OP_SELL when f=-1.
NOTE: Regarding the color of the orders I put them in an array
color COL[2]= {clrBlue,clrRed};
then, having OP_TYPE, I set
color COLOR=COL[OP_TYPE];
Step 2. Similarly, I set the Order Open Price as
double OOP = int(0.5*((1+f)*Ask+(1-f)*Bid));
which takes value OOP=Ask when f=1, while OOP=Bid when f=-1.
Step 3. Then, given my desired Stop Loss in pips (an external POSITIVE parameter of my EA, I named sl) I make sure that sl > SLS. In other words, I check
if (sl <= mSLS) // I set my sl as the minimum allowed
{
sl = 1 + mSLS;
}
Step 4. Then I calculate the Stop-Loss Price of the order as
double SLP = OOP - f * sl * Point;
Step 5. Given my desired Take Profit in pips (an external POSITIVE parameter of my EA, I named tp) I calculate the Take-Profit Price (TPP) of the order as
double TPP = OOP + f * tp * Point;
OBSERVATION: I can not affirm, but, according to mql4 documentation, the minimum distance rule between the stop-loss limit prices and the open price also applies to the take profit limit price. In this case, a "tp" check-up needs to be done, similar to that of the sl check-up, above. that is, before calculating TPP it must be executed the control lines below
if (tp <= mSLS) // I set my tp as the minimum allowed
{
tp = 1 + mSLS;
}
Step 5. I call for order opening with a given lot size (ls) and slippage (slip) on the operating currency pair (from where I get the Ask and Bid values)
float ls = 0.01;
int slip = 3; //(pips)
int order = OrderSend(Symbol(),OP_TYPE,ls,OOP,slip,SLP,TPP,"",0,0,COLOR);
Note that with these few lines it is easy to build a function that opens orders of any type under your command, in any currency pair you are operating, without receiving error message 130, passing to the function only 3 parameters: f, sl and tp.
It is worth including in the test phase of your EA a warning when the sl is corrected for being less than the allowed, this will allow you to increase its value so that it does not violate the stop-loss minimum value rule, while you have more control about the risk of its operations. Remember that the "sl" parameter defines how much you will lose if the order fails because the asset price ended up varying too much in the opposite direction to what was expected.
I hope I could help!
Whilst the other two answers are not necessarily wrong (and I will not go over the ground they have already covered), for completeness of answers, they fail to mention that for some brokers (specifically ECN brokers) you must open your order first, without setting a stop loss or take profit. Once the order is opened, use OrderModify() to set you stop loss and/or take profit.
I am making a roguelike in Love2D as a hobby project. My approach is to try and use as much of the native capabilities of Lua and the Love2D (0.10.1) API as possible, without relying on fancy libraries like middleclass or HUMP, so as to learn more about the language.
After reading PiL's chapters on OOP and seeing the power there, I decided to set up a Mob class (using metamethods to emulate class functionality) that encompasses the players, monsters, and other NPCs (anything that can move). So, far, it's working beautifully, I can create all kinds of instances easily that share methods and all that stuff. But there's a lot of things I don't know how to do, yet, and one of them is holding my prototype up from further progress.
Setting up collision with the map itself wasn't too bad. My maps are tables full of tables full of integers, with 0 being the floor. The game draws "." and "#" and "+" and such to denote various inanimate objects, from each table. Player 1 moves using the numpad, and their position is tracked by dividing their raw pixel position by 32 to create a grid of 32x32 "tiles". Then, inside love.keypressed(key), I have lines like:
if key == "kp8" and currentmap[player1.grid_y - 1][player1.grid_x] == 0 then
player1.grid_y = player1.grid_y - 1
and so on, with elseifs for each key the player can press. This prevents them from walking through anything that isn't an open floor tile in the map itself.
But, I'm trying to implement some kind of "collision detection" to prevent MOBs from walking through each other and to use in writing the rules for combat, and this is trickier. I had a method in place to calculate the distance between mobs, but I'm told this might eventually cause rounding errors, plus it had to be written for each combination of mobs I want to test, individually.
What I'd like to know is: Is there a known (preferably elegant) way to get all instances of a particular class to pass some number of values to a table?
What I'd like to do is "ask" every Mob on a given map where they are, and have them "report" self.grid_x and self.grid_y to another layer of map that's just for tracking mobs (1 if self.is_here is true, 0 if not, or similar), that gets updated every turn. Then, I could implement collision rules based on coordinates being equal, or maybe a foo.is_here flag or something.
I have only vague ideas about how to proceed, however. Any help would be appreciated, including (and maybe especially) feedback as to a better way to do what I'm trying to do. Thanks!
A simple idea is to store "who is here" information for every cell of the field and update this information on every move of every object.
function create_game_field()
-- initialize a table for storing "who is here" information
who_is_here = {}
for y = 1,24 do
who_is_here[y] = {}
for x = 1,38 do
who_is_here[y][x] = 0
end
end
end
function Mob:can_move(dx, dy)
local u = currentmap[self.y + dy][self.x + dx]
local v = who_is_here[self.y + dy][self.x + dx]
if u == 0 and v == 0 then
return true
else
end
end
function Mob:move(dx, dy)
-- update "who is here"
who_is_here[self.y][self.x] = 0
self.x, self.y = self.x + dx, self.y + dy
who_is_here[self.y][self.x] = 1
end
function Mob:who_is_there(dx, dy) -- look who is standing on adjacent cell
return who_is_here[self.y + dy][self.x + dx] -- return mob or nil
end
function Mob:roll_call()
who_is_here[self.y][self.x] = 1
end
Usage example:
-- player1 spawns in at (6,9) on the grid coords
player1 = Mob:spawn(6,9)
-- player1 added to who_is_here
player1:roll_call()
Then, in love.keypressed(key):
if key == "kp8" and player1:can_move(0, -1) then
player1:move(0, -1)
end
There are a few ways you could get all your instances data but one of the simpler ones is probably to have them all be added to a table when they are created. Providing you add the entire table for that instance, all the values will update in the main table because it acts like a collection of pointers.
function mob:new( x, y, type )
self.x = 100
self.y = 200
self.type = type
-- any other declarations you need
table.insert(allMobs, self)
return self
end
Here we insert all the mobs into the table 'allMobs'. Once we have that we can simply iterate through and get all our coordinates.
for i, v in ipairs(allMobs) do
local x, y = v.x, v.y
-- Do whatever you need with the coordinates. Add them to another table, compare
-- them to others, etc.
end
Now we have a table with all our mobs in it and a way to access each of their positions. If you have any further inquiries then let me know.
I am using Dentaku gem to solve little complex expressions like basic salary is 70% of Gross salary. As the formulas are user editable so I worked on dentaku.
When I write calculator = Dentaku::Calculator.new to initialize and then enter the command calculator.evaluate("60000*70%") then error comes like below:
Dentaku::ParseError: Dentaku::AST::Modulo requires numeric operands
from /Users/sulman/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/dentaku-2.0.8/lib/dentaku/ast/arithmetic.rb:11:in `initialize'
I have array is which formula is stored like: ["EarningItem-5","*","6","7","%"] where EarningItem-5 is an object and has value 60000
How can I resolve such expressions?
For this particular case you can use basic_salary = gross_salary * 0.7
Next you need to create the number field in your views which accepts 0..100 range. At last, set up the after_save callback and use this code:
model
after_create :percent_to_float
protected
def percent_to_float
self.percent = percent / 100.0
self.save
end
edit:
Of course, you can simply use this formula without any callbacks:
basic_salary = gross_salary / 100.0 * 70
where 70 is user defined value.
Dentaku does not appear to support "percent". Try this instead
calculator.evaluate('60000 * 0.7')
First off, the column in the database table is a DECIMAL with a length of 10,4.
If I do this on the console or even in the controller, the result is correct:
rate = (1 / 0.7126) * 1.0883
but if I do this, it doesn't work:
rate = (1 / from_rate) * to_rate
The result is simply the value of to_rate.
from_rate and to_rate are the results of database queries and the values are correct, if I log the class using .class the result is BigDecimal, so I have no idea why this calculation doesn't work as intended.
I've tried explicitly converting using to_d and BigDecimal.new but they don't seem to make a difference.
From evidence, it looks like the integer division instance method (invoked by / as in (1 / from_rate) returns an integer result when the argument (the divisor) is BigDecimal, so in this case it's returning the integer value 1. This isn't a problem when the argument is a float as in those cases integer division does return a float.
You may be able to circumvent this problem by just using the float divisor... do that by specifying 1.0 (a float) as the dividend.
rate = (1.0 / from_rate) * to_rate
Or alternatively you can convert the from_rate value into a float.
rate = (1 / from_rate.to_f) * to_rate
I am trying to save money format in laravel 5.1.
Here is table price define:
$table->decimal(price,6,2);
For instance ; when 1.000,50 Turkish Liras saving to MySQL this format 1.00
How can solve this issue?
You can try defining your price like this
$table->decimal('price',9,3);
Where,
9 is the precision, ie 1234567.89 has a precision of 9
3 is the number of decimal places, ie 123456.789 has a scale of 3
In other words, if we use less decimal-places than 3, we can use remaining for real-number places.
You can refer to this link for about precision and scale of database
How do I interpret precision and scale of a number in a database?
I would suggest not using a float value to store currency as decimals, since floats don't act exactly as you would expect them to, due to the way they are stored in the system.
You would be much better off storing the value in "kuruş" (the subunit of Turkish Lira), as it will be much, much easier in the long run.
In other words, storing the lowest unit you think will be ever required, like storing Centi-meters instead of Meters (Centi is originally Greekish name for "0.01" number).
Secondly, if you're using Eloquent you can use mutators/accessors on the Model e.g.
public function getPriceAttribute($price)
{
return $price / 100;
}
public function setPriceAttribute($price)
{
$this->attributes['price'] = $price * 100;
}
That way you don't have to manually convert the price.
Update
If you're using Laravel 9 or above, you can use the new Attribute syntax instead:
use Illuminate\Database\Eloquent\Casts\Attribute;
protected function price(): Attribute
{
return Attribute::make(
get: fn ($price) => $price / 100,
set: fn ($price) => $price * 100,
);
}
Illuminate blueprints do not support money columns. AFAIK, the money column type itself is only supported in a couple of DBMSes.
What you can do is issue an ALTER TABLE statement to the database after the initial CREATE statement:
Schema::create('my_table', function(Blueprint $table) {
$table->decimal('my_money_column', 999, 2);
// ... the rest of the column definitions
});
DB::statement("
ALTER TABLE my_table ALTER COLUMN my_money_column
SET DATA TYPE MONEY;
");
Beware, though, as this will (probably) break cross-DBMS compatibility of your migration scripts.