average

What's the most efficient way to create a moving average or rolling sum in R? How do you do the rolling function along with a "group by"? While zoo is great, sometimes there are simpler ways. If you data behaves nicely, and is evenly spaced, the embed() function effectively lets you create multiple lagged version of a time series. If you look inside the VARS package for vector auto-regression, you will see that the package author chooses this route. For example, to calculate the 3 period rolling average of x, where x = (1 -> 20)^2: > x <- (1:20)^2 > embed (x, 3) [,1] [,2] [,3] [1,] 9 4 1 [2,]

Time to test your math skills... I'm using php to find the average of $num1, $num2, $num3 and so on; upto an unset amount of numbers. It then saves that average to a database. Next time the php script is called a new number is added to the mix. Is there a math (most likely algebra) equation that I can use to find the average of the original numbers with the new number included. Or do I need to save the original numbers in the database so I can query them and re-calculate the entire bunch of numbers together? If what you mean by average is mean and you don't want to store all numbers then store

This question already has an answer here: Calculate speed per sec and time left of sending a file using sockets tcp c# 3 answers im trying to calculate the transfer file speed per second using the average i took the different between the sent bytes sum and the prevSum 5 times per second does the code below give me the correct speed? should i change the rate array size ? or should i change Thread.Sleep(value) ? im so confused because each time a change a little thing the speed value changes.. what's the correct solution for that ?? static long prevSum = 0; static long[] rate = new long[5];

I'm trying to debug a program in ruby that is meant to compute and print the average length of words in an array. words = ['Four', 'score', 'and', 'seven', 'years', 'ago', 'our', 'fathers', 'brought', 'forth', 'on', 'this', 'continent', 'a', 'new', 'nation', 'conceived', 'in', 'Liberty', 'and', 'dedicated', 'to', 'the', 'proposition', 'that', 'all', 'men', 'are', 'created', 'equal'] word_lengths = Array.new words.each do |word| word_lengths << word_to.s end sum = 0 word_lengths.each do |word_length| sum += word_length end average = sum.to_s/length.size puts "The average is " + average.to_s

This question already has an answer here: Mongo average aggregation query with no group 3 answers Suppose that I have a collection like this: { _id: 1, city: "New York", state: "NY", murders: 328 } { _id: 2, city: "Los Angeles", state: "CA", murders: 328 } ... The collection shows us the number of murders in all cities of USA. I'd like to calculate the average of murders in all the country. I tried to use $group: db.murders.aggregate([{$group: {_id:"$state", pop: {$avg:"$murders"} } }]) But I get as result the murders by state: { "_id" : "NY", "murders" : 200 } { "_id" : "NJ", "murders" : 150