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I have to data frames with X, Y, and Z coordinates. I want to find the distance between all of the points in the two data frames. (Like the distance between entry A1 and every entry in B, A2 and every entry in B, and so on, and vice versa). I basically did this:
1.) Wrote a function that calculates the distance between two points.
2.) Used the distanceFinder function to create a function that finds the distance between one point in a group, and every other point in the opposite group.
3.) Created a function called bigDistance() that calls filter() on every entry in one group, and appends the results to an empty data frame through a for loop until it's completed.
This code takes about 2 minutes to run on the file I'm experimenting with, and I just found out that I have to translate this algorithm to PHP... so I guess this is kind of an optimization question, because I feel like PHP would be way slower at making these computations than R? Sorry if people find this "off-topic" but yeah, super new to programming and Big O notation and stuff, so any tips would be amazing! Thanks!
The dist function does exactly what you are looking for.
myDf <- data.frame(
x = rnorm(8),
y = rnorm(8),
z = rnorm(8)
)
dist(myDf)
# 1 2 3 4 5 6 7
# 2 3.0457054
# 3 1.7260658 3.2107845
# 4 1.2839101 3.4596211 2.9451175
# 5 1.5656231 4.0154389 2.3421445 2.3612348
# 6 1.9294650 1.6655718 1.7977887 2.8726174 2.5815296
# 7 2.1842743 3.5274692 3.8552701 1.0984651 2.9951244 3.3220919
# 8 1.4795857 3.5364663 0.5567753 2.7033371 1.9226225 2.0631788 3.6624082
It seems to be pretty fast as well (73ms on average)
library(microbenchmark)
mb <- microbenchmark(dist(myDf))
mb
# Unit: microseconds
# expr min lq mean median uq max neval
# dist(myDf) 70.436 71.453 77.4083 72.978 82.133 172.911 100
autoplot(mb)
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I need help I have the following 2 points on the map point A lat1/long1 and point B lat2/long2 in google map I have distance, arrived_time, bearingradians and speed.
With these data how can I get a estimated latitude longitude (google map format) to the next point on 10 minutes,20,30 and 40 minutes ?, having start and end point.
Point A
lat1=37.78472
lon1=-122.39913
Point B
lat2=37.78240
lon2=-121.23208
bearingradians=270
distance=102 KM
arrive_time=50 minutes
speed =122 KM/H
example:
http://hmarina.sytes.net/mapagoogle.jpg
What I need you to calculate the nexts points, I going to use PHP, or where should I start
Thank you
There are multiple ways to calculate this. Some of them are quite complex.
You could use Vincenty's formula, which is often used for bearing and distance calculations.
The formula needs Long/Lat of the starting point, the bearing and a distance.
I doubt, that you want to reimplement this algo, so here you go: Implementing Vincenty's Formula in PHP
Another solution could be to use vectors to calculate the destination points along a great-circle given distance and bearing from start point. This approach might be a bit easier, then to work with spherical trigonometry. http://www.movable-type.co.uk/scripts/latlong-vectors.html and https://stackoverflow.com/a/1739066/1163786
Another one is to calculate the intermediate points on a great-circle.
http://williams.best.vwh.net/avform.htm#Intermediate
Let's use Vincenty here and re-calc your end-point, given a starting-point, bearing and distance:
a starting point: Point A lat1=37.78472; lon1=-122.39913;
the bearing: approx. 89
the distance: 102 km
Result: Latitude: 37°47′42″N 37.79506902, Longitude: 121°14′28″W -121.24119021
That is pretty close your Point B.
Now, you want to determine the future position (lang/lat) by calculating the distance you will travel based on your current speed and your known time interval.
In other words, your next point is 10 minutes from the starting point given speed 122 km/h and 89 bearing.
Calculate new distance: 122 km/h = 2033.33 m/min, so in 10 minutes: 20333.33 m = 20,333 km approx.
You new data for the formula:
a starting point, here: Point A lat1=37.78472; lon1=-122.39913;
the bearing: approx. 89
the distance: 20,333 km
And re-run vincenty with these values to get Lat/Long...
This might be of help:
PHP library for geo/nav calculations
Google Maps API v3 provides Navigation Helper methods
You have: speed = 122Km/h => You can calculate 10 minute walked (n _km)
You can calculate distance with 2 point distance
sqrt((lat1 - lat2)^2 + (lng1-lng2)^2);
you have distance and lat1, how to calculate lat2:
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I'm building a browser game which you can shoot missiles on factories.
This is example of a similar SQL table:
user_ID iron steel metal gold
1 21 30 39 25
2 7 10 25 50
I need each missile to destroy 1 factory.
For example I shoot 10 missile, so 10 factories are destroyed. But I need it to have completely randomly and even.
The problem is if according to this SQL table, if I shoot for example 40 missile on user_ID '2'.
In best case I destroy 10 factories of each kind. But how can I do it when I don't know if there is enough of each kind?
First, divide the number of missiles by the number of factory types that have at least 1 factory. If all the types have at least this many factories, subtract this from each column.
If any of the types have less than this, they'll be totally wiped out. Reduce them to 0 and subtract their original totals from the number of missiles. Then start again, using just the remaining missiles.
Repeat this until you use up all the missiles or all factories are wiped out.
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I have a voting table called product_reviews, with a field that is ENUM from 1 to 5 called rating.
I want to get average rating from all rows with product_id 1665. I am using a star rating system so the average cannot be with decimals. Must be a number from 1 to 5.
Thank you very much.
SELECT round(avg(rating)) as average_review,
count(rating) as number_of_reviews
FROM product_reviews
WHERE product_id = 1665
You need to use round here since avg will return a value between 1.0 and 5.0, and if you use floor or ceil you're effectively eliminating 1 or 5 from the possible results unless all reviews on the product have that score.
Also, you'll alienate your users if they can openly see a product got 50 reviews with 1 star, and 1 review with 2 stars, and you're showing an average score of 2 stars next to that. It'll make your site seem unreliable which is usually not a good thing for a site that contains reviews. For this reason most star rating systems are also capable of showing partial stars to make it more precise.
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3rd grade question:
How do you calculate the distance between two points on a flat surface?
I have been going through the Google_Results and it seems everything i find applies to Long/Lat and not a flat surface.
I'm working on making ObjectA choose between ObjetsC,D,E... , select the closest one and move toward it. So I have to loop through my SQL table, pull out what's in range, and loop through the results to calculate distances.
Any help with this math I haven't had to remember in years would be appreciated.
You will need to use a Euclidean distance formula (specifically for 2 dimensions). Basically the formula is:
d = sqrt((x1 - x2)^2 + (y1 - y2)^2)
d is your final distance
sqrt is the square root (the sqrt() function in PHP)
x1 and y1 are your x-y coordinates for your first point
x2 and y2 are your x-y coordinates for your second point
^2 means raise to the second power (use the pow() function for PHP)
Pythagoras was the Greek philosopher who developed the Pythagorean Theorem, which can be used to derive the 2-dimensional distance formula (which is different from Euclid's derivation).
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This is a bit of a puzzle. Look at the sum and result below:
$markTotal += ($session['Mark'] / 100 * $session['SessionWeight']);
Result on Browser:
Module: CHI2550 - Modern Database Applications 41.2 (this is $markTotal)
Session: AAB 72(this is $session['Mark']) 20% (this is $session['SessionWeight'])
Session: AAE 67(this is $session['Mark']) 40% (this is $session['SessionWeight'])
As you can see the answer to the calculation above is right, the answer is 41 .2 as it adds up the two session marks, divide by 100 and then times it by the total amount of the percentage.
But I want to include a total mark where except it is out of the total session percentage (60% for above example), it is out of a 100% but I can not work as simple as that as in above example one session is worth more than other. I have worked out that the answer for the total mark of the above example out of 100% should be 69, but how do I achieve this in my calculation.
Thank you and any help is much appreciated :)
You'd need to add up the total marks as well. So if session AAB has 90 total marks available (and the student got 72) and AAE has 80 marks (and got 67) then it'd be
(72) + (67) 14.4 26.8 41.2
(--) * 0.2 + (--) * 0.4 = ---- + ---- = ---- = 79.23%
(90) + (80) 18 34 52