median

I'd like to calculate the median value in a numeric row. How can I do that in SQLite 4? Let's say that the median is the element in the middle of an ordered list. SQLite (4 or 3) does not have any built-in function for that, but it's possible to do this by hand: SELECT x FROM MyTable ORDER BY x LIMIT 1 OFFSET (SELECT COUNT(*) FROM MyTable) / 2 When there is an even number of records, it is common to define the median as the average of the two middle records. In this case, the average can be computed like this: SELECT AVG(x) FROM (SELECT x FROM MyTable ORDER BY x LIMIT 2 OFFSET (SELECT (COUNT(*

I have a process that generates values and that I observe. When the process terminates, I want to compute the median of those values. If I had to compute the mean, I could just store the sum and the number of generated values and thus have O(1) memory requirement. How about the median? Is there a way to save on the obvious O(n) coming from storing all the values? Edit: Interested in 2 cases: 1) the stream length is known, 2) it's not. You are going to need to store at least ceil(n/2) points, because any one of the first n/2 points could be the median. It is probably simplest to just store the

I have a data.table called enc.per.day for encounters per day. It has 2403 rows in which a date of service is specified and the number of patients seen on that day. I wanted to see the median number of patients seen on any type of weekday. enc.per.day[,list(patient.encounters=median(n)),by=list(weekdays(DOS))] That line gives an error Error in [.data.table (enc.per.day, , list(patient.encounters = median(n)), : columns of j don't evaluate to consistent types for each group: result for group 4 has column 1 type 'integer' but expecting type 'double' The following all work well tapply(enc.per.day

Note: Please don't interpret this as "homework question." This is just a thing I curious to know :) The median of five is sometimes used as an exercise in algorithm design and is known to be computable using only 6 comparisons . What is the best way to implement this "median of five using 6 comparisons" in C# ? All of my attempts seem to result in awkward code :( I need nice and readable code while still using only 6 comparisons. public double medianOfFive(double a, double b, double c, double d, double e){ // // return median // return c; } Note: I think I should provide the "algorithm" here

Wikipedia says: Selection algorithms: Finding the min, max, both the min and max, median , or even the k-th largest element can be done in linear time using heaps. All it says is that it can be done, and not how. Can you give me some start on how this can be done using heaps? You would use a min-max-median heap to find the min, max and median in constant time (and take linear time to build the heap). You can use order-statistics trees to find the kth smallest/largest value. Both of these data structures are described in this paper on min-max heaps [pdf link] . Min-max heaps are binary heaps

I am trying to implement Median of Medians in Java for a method like this: Select(Comparable[] list, int pos, int colSize, int colMed) list is a list of values of which to find a specified position pos is the specified position colSize is the size of the columns that I create in the first stage colMed is the position in those columns that I use as the medX I am not sure which sorting algorithm would be the best to use or how to implement this exactly.. I don't know if you still need this problem solved, but http://www.ics.uci.edu/~eppstein/161/960130.html has an algorithm: select(L,k) { if (L