reduce

I'm trying to concatenate a Seq of Seqs. I can do it with apply concat . user=> (count (apply concat (repeat 3000 (repeat 3000 true)))) 9000000 However, from my limited knowledge, I would assume that the use of apply forces the lazy Seq to be realised, and that doesn't seem right for very large inputs. I'd rather do this lazily if I can. So I thought that using reduce would do the job. user=> (count (reduce concat (repeat 3000 (repeat 3000 true)))) But this results in StackOverflowError clojure.lang.RT.seq (RT.java:484) I'm surprised because I would have thought that the semantics of reduce

As far as I understand, the reduce function takes a list l and a function f . Then, it calls the function f on first two elements of the list and then repeatedly calls the function f with the next list element and the previous result. So, I define the following functions: The following function computes the factorial. def fact(n): if n == 0 or n == 1: return 1 return fact(n-1) * n def reduce_func(x,y): return fact(x) * fact(y) lst = [1, 3, 1] print reduce(reduce_func, lst) Now, shouldn't this give me ((1! * 3!) * 1!) = 6 ? But, instead it gives 720 . Why 720 ? It seems to take the factorial of

Is there any way to map / reduce / filter /etc a Set in JavaScript or will I have to write my own? Here's some sensible Set.prototype extensions Set.prototype.map = function map(f) { var newSet = new Set(); for (var v of this.values()) newSet.add(f(v)); return newSet; }; Set.prototype.reduce = function(f,initial) { var result = initial; for (var v of this) result = f(result, v); return result; }; Set.prototype.filter = function filter(f) { var newSet = new Set(); for (var v of this) if(f(v)) newSet.add(v); return newSet; }; Set.prototype.every = function every(f) { for (var v of this) if (!f(v

In MPI, I am doing a reduce operation(minimum) on a value. This works fine, but how do I grab the processor number that the minimum came from and solicit that processor for more information(or send the additional data with the reduce operation)? Jonathan Dursi If you don't mind paring each value locally with an integer index (filled in this case with the value of the local rank), you can use the MPI_MINLOC or MPI_MAXLOC builtin operations for reduce; or it's fairly easy to write your own MPI reduction operator to include things like multiple indices, etcc Updated to add: With the builtin

I gather data from 4 df's and would like to merge them by rownames. I am looking for an efficient way to do this. This is a simplified version of the data I have. df1 <- data.frame(N= sample(seq(9, 27, 0.5), 40, replace= T), P= sample(seq(0.3, 4, 0.1), 40, replace= T), C= sample(seq(400, 500, 1), 40, replace= T)) df2 <- data.frame(origin= sample(c("A", "B", "C", "D", "E"), 40, replace= T), foo1= sample(c(T, F), 40, replace= T), X= sample(seq(145600, 148300, 100), 40, replace= T), Y= sample(seq(349800, 398600, 100), 40, replace= T)) df3 <- matrix(sample(seq(0, 1, 0.01), 40), 40, 100) df4 <-

What is the most idiomatic way to achieve something like the following, in Haskell: foldl (+) 0 [1,2,3,4,5] --> 15 Or its equivalent in Ruby: [1,2,3,4,5].inject(0) {|m,x| m + x} #> 15 Obviously, Python provides the reduce function, which is an implementation of fold, exactly as above, however, I was told that the 'pythonic' way of programming was to avoid lambda terms and higher-order functions, preferring list-comprehensions where possible. Therefore, is there a preferred way of folding a list, or list-like structure in Python that isn't the reduce function, or is reduce the idiomatic way of