reduce

one-liner reduce in Python3

由 南楼画角 提交于 2019-11-30 16:45:39
In Python3, I am looking for a way to compute in one line a lambda function called on elements two by two. Let’s say I want to compute the LCM of a list of integers, this can be done in one line in Python2 : print reduce(lambda a,b: a * b // gcd(a, b), mylist) Is it possible to do the same in one line Python3 (implied, without functools.reduce )? In Python3 I know that filter , map and reduce are gone. I don’t feel I need filter and map anymore because they can be written in Python3 in a shorter and more clear fashion but I thought I could find a nice replacement for reduce as well, except I

Does R have something equivalent to reduce() in Python?

由 安稳与你 提交于 2019-11-30 12:58:44
问题 That is : "Apply function of two arguments cumulatively to the items of sequence, from left to right, so as to reduce the sequence to a single value. " 回答1: Yes, it's called Reduce . An example: Reduce(paste, LETTERS[1:5]) [1] "A B C D E" Reduce(sum, 1:5) [1] 15 #List arguments work the same Reduce(sum, list(1, 2, 3, 4, 5)) [1] 15 For more information about functional programming in R see the help file for ?funprog , an alias for ?Reduce 回答2: Yes. See http://stat.ethz.ch/R-manual/R-patched

Count the number of true members in an array of boolean values

由 ↘锁芯ラ 提交于 2019-11-30 11:42:00
New to javascript and I'm having trouble counting the number of trues in an array of boolean values. I'm trying to use the reduce() function. Can someone tell me what I'm doing wrong? //trying to count the number of true in an array myCount = [false,false,true,false,true].reduce(function(a,b){ return b?a++:a; },0); alert("myCount ="+ myCount); // this is always 0 Seems like your problem is solved already, but there are plenty of easier methods to do it. Array.prototype.filter() - the easiest one, in my opinion. console.log([true,false,true,false,true].filter(v => v).length); or even simplier:

Reduce array to set in Swift

由 假如想象 提交于 2019-11-30 10:38:17
问题 I am trying to reduce an array of objects to a set in Swift and this is my code: objects.reduce(Set<String>()) { $0.insert($1.URL) } However, I get an error: Type of expression is ambiguous without more context. I do not understand what the problem is, since the type of URL is definitely String. Any ideas? 回答1: You don't have to reduce an array to get it into a set; just create the set with an array: let objectSet = Set(objects.map { $0.URL }) . 回答2: With Swift 5.1, you can use one of the

NameError: global name 'reduce' is not defined

由 不问归期 提交于 2019-11-30 07:46:36
问题 I'm new to Python. Would you please tell me what's wrong with the following code? When I run it, I got an error message of "NameError: global name 'reduce' is not defined". I asked Goolge but it's useless. :( def main(): def add(x,y): return x+y reduce(add, range(1, 11)) if __name__=='__main__': main() 回答1: I'm going to guess that: You are using Python 3, and You are following a tutorial designed for Python 2. The reduce function, since it is not commonly used, was removed from the built-in

Using map reduce in CouchDB to output fewer rows

由 我的未来我决定 提交于 2019-11-30 06:26:05
问题 Lets say you have two document types, customers and orders . A customer document contains basic information like name, address etc. and orders contain all the order information each time a customer orders something. When storing the documents, the type = order or the type = customer. If I do a map function over a set of 10 customers and 30 orders it will output 40 rows. Some rows will be customers, some will be orders. The question is, how do I write the reduce, so that the order information

Pyspark RDD ReduceByKey Multiple function

由 妖精的绣舞 提交于 2019-11-30 05:59:59
问题 I have a PySpark DataFrame named DF with (K,V) pairs. I would like to apply multiple functions with ReduceByKey. For example, I have following three simple functions: def sumFunc(a,b): return a+b def maxFunc(a,b): return max(a,b) def minFunc(a,b): return min(a,b) When I apply only one function, e.g,, following three work: DF.reduceByKey(sumFunc) #works DF.reduceByKey(maxFunc) #works DF.reduceByKey(minFunc) #works But, when I apply more than one function, it does not work, e.g., followings do

Creating a Dictionary from a List of 2-Tuples

由 隐身守侯 提交于 2019-11-30 05:33:00
问题 I have a list of 2-tuples like this: l = [('a', 1), ('b', 2)] and I want to be able to map this onto a dictionary object, so that I can do something like l.a #=> 1 So I tried this, but why does it fail? d = reduce(lambda y,x : y.update({x[0]:x[1]}),l,{}) This gives the error: AttributeError: 'NoneType' object has no attribute 'update' What am I doing wrong? 回答1: >>> l = [('a', 1), ('b', 2)] >>> d = dict(l) >>> d['a'] 1 回答2: Why not just do this: d = dict(l) Also, to answer your question, your

Does R have something equivalent to reduce() in Python?

由 自古美人都是妖i 提交于 2019-11-30 04:28:44
That is : "Apply function of two arguments cumulatively to the items of sequence, from left to right, so as to reduce the sequence to a single value. " Andrie Yes, it's called Reduce . An example: Reduce(paste, LETTERS[1:5]) [1] "A B C D E" Reduce(sum, 1:5) [1] 15 #List arguments work the same Reduce(sum, list(1, 2, 3, 4, 5)) [1] 15 For more information about functional programming in R see the help file for ?funprog , an alias for ?Reduce Yes. See http://stat.ethz.ch/R-manual/R-patched/library/base/html/funprog.html 来源： https://stackoverflow.com/questions/7413819/does-r-have-something

Understanding Eloquent Javascript's Reduce function

由 烂漫一生 提交于 2019-11-30 04:05:33
In Eloquent Javascript , the author asks the reader to write a function countZeroes , which takes an array of numbers as its argument and returns the amount of zeroes that occur in it as another example for the use of the reduce function. I know that the concept of the reduce function is to take an array and turn it to a single value. what the ternary operator is doing which is the essential portion of the function. I don't know where the arguments for the counter function are coming from. From the book: function countZeroes(array) { function counter(total, element) { // Where are the
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