reduce

Is it valid to reduce on an empty set of sets?

由 血红的双手。 提交于 2019-12-04 01:55:23
Shouldn't this work? > val setOfSets = Set[Set[String]]() setOfSets: scala.collection.immutable.Set[Set[String]] = Set() > setOfSets reduce (_ union _) java.lang.UnsupportedOperationException: empty.reduceLeft at scala.collection.TraversableOnce$class.reduceLeft(TraversableOnce.scala:152) [...] Reduce (left and right) cannot be applied on an empty collection. Conceptually: myCollection.reduce(f) is similar to: myCollection.tail.fold( myCollection.head )( f ) Thus the collection must have at least one element. This should do what you want: setOfSets.foldLeft(Set[String]())(_ union _) Although I

Javascript: Using reduce() to find min and max values?

由 孤街醉人 提交于 2019-12-03 23:30:52
问题 I have this code for a class where I'm supposed to use the reduce() method to find the min and max values in an array. However, we are required to use only a single call to reduce. The return array should be of size 2, but I know that the reduce() method always returns an array of size 1. I'm able to obtain the minimum value using the code below, however I don't know how to obtain the max value in that same call. I assume that once I do obtain the max value that I just push it to the array

Spark: groupBy taking lot of time

由 一曲冷凌霜 提交于 2019-12-03 22:59:14
问题 In my application when taking perfromance numbers, groupby is eating away lot of time. My RDD is of below strcuture: JavaPairRDD<CustomTuple, Map<String, Double>> CustomTuple: This object contains information about the current row in RDD like which week, month, city, etc. public class CustomTuple implements Serializable{ private Map hierarchyMap = null; private Map granularMap = null; private String timePeriod = null; private String sourceKey = null; } Map This map contains the statistical

Where is the “Fold” LINQ Extension Method?

由 a 夏天 提交于 2019-12-03 22:01:20
I found in MSDN's Linq samples a neat method called Fold() that I want to use. Their example: double[] doubles = { 1.7, 2.3, 1.9, 4.1, 2.9 }; double product = doubles.Fold((runningProduct, nextFactor) => runningProduct * nextFactor); Unfortunately, I can't get this to compile, either in their example or in my own code, and I can't find anywhere else in MSDN (like Enumerable or Array extension methods) that mention this method. The error I get is a plain old "don't know anything about that" error: error CS1061: 'System.Array' does not contain a definition for 'Fold' and no extension method

filter、map、reduce、lambda 使用总结

由 安稳与你 提交于 2019-12-03 18:24:16
1. lambda 1.1简述 lambda ： 这是Python支持一种有趣的语法，它允许你快速定义单行的最小函数，类似与C语言中的宏，这些叫做lambda的函数，是从LISP借用来的，可以用在任何需要函数的地方： 1.2 实例 >>> test = lambda x, y: x + y >>> test(1,2) 3 2. filter 2.1简述 filter(function, sequence)： 对sequence中的item依次执行function(item)，将执行结果为True的item组成一个List/String/Tuple（取决于sequence的类型）返回. 2.2 实例 >>> tt = (1,2,3,4,) >>> filter(lambda x:x == 2, tt) (2,) 3. map 3.1简介 map(function, sequence) ： 对sequence中的item依次执行function(item)，见执行结果组成一个List返回 3.2 实例 >>> map(lambda x: x*x, range(1,4)) [1, 4, 9] >>> 4.reduce 4.1简介 reduce(function, sequence, starting_value)：对sequence中的item顺序迭代调用function

Reduce function with three parameters

由 限于喜欢 提交于 2019-12-03 18:01:14
问题 How does reduce function work in python3 with three parameters instead of two. So, for two, tup = (1,2,3) reduce(lambda x, y: x+y, tup) I get this one. This would just sum up all the elements in tup . However, if you give reduce function three parameters like this below, tup = (1,2,3) reduce(lambda x, y: x+y, tup, 6) this would give you a value of 12 . I checked up on the documentation for python3 and it says the third argument is an initializer. That said, then what is the default

Video Compression ios : Reduce the size of a video usin AVAssetWriter

由 寵の児 提交于 2019-12-03 17:03:10
I am Successful in encoding a series of image captured by AVCaptureVideoPreviewLayer of AVFoundation Framework into a Video using AVAssetWriter and AVAssetWriterInput. But the size of the video is too large, Can anyone of you suggest me a tutorial or atleast a direct me in this case or give me the correct Video output Settings for video compression. I am using the following VideoOutputSetting. videoOutputSettings = @{ AVVideoCodecKey: AVVideoCodecH264, AVVideoWidthKey: [NSNumber numberWithInt:width], AVVideoHeightKey: [NSNumber numberWithInt:height], AVVideoCompressionPropertiesKey: @{

Compose example in Paul Graham's ANSI Common Lisp

由 北慕城南 提交于 2019-12-03 16:27:01
问题 Can anybody explain an example in Paul Graham's ANSI Common Lisp page 110? The example try to explain the use &rest and lambda to create functional programming facilities. One of them is a function to compose functional arguments. I cannot find anything explaining how it worked. The code is as follows: (defun compose (&rest fns) (destructuring-bind (fn1 . rest) (reverse fns) #'(lambda (&rest args) (reduce #'(lambda (v f) (funcall f v)) rest :initial-value (apply fn1 args))))) The usage is:

Using Java 8 Stream Reduce to return List after performing operation on each element using previous elements values

由 元气小坏坏 提交于 2019-12-03 15:27:33
I'm new to Streams and Reduce so I'm trying it out and have hit a problem: I have a list of counters which have a start counter and end counter. The startcounter of an item is always the endcounter of the previous. I have a list of these counters listItems which I want to loop through efficiently, filter out inactive records and then reduce the list into a new List where all the StartCounters are set. I have the following code: List<CounterChain> active = listItems.stream() .filter(e -> e.getCounterStatus() == CounterStatus.ACTIVE) .reduce(new ArrayList<CounterChain>(), (a,b) -> { b

Use global variable in reudcer class

由 谁都会走 提交于 2019-12-03 14:08:43
问题 I need to use global variable in my mapreduce program how to set it in following code and use global variable in reducer. public class tfidf { public static tfidfMap.............. { } public static tfidfReduce............. { } public static void main(String args[]) { Configuration conf=new Configuration(); conf.set("",""); } } 回答1: Template code could look something like this (Reducer not shown but is the same principal) import java.io.IOException; import org.apache.hadoop.conf.Configuration;
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