apply | 易学教程

calculate row sum and product in data.frame

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问题 I would like to append a columns to my data.frame in R that contain row sums and products Consider following data frame x y z 1 2 3 2 3 4 5 1 2 I want to get the following x y z sum prod 1 2 3 6 6 2 3 4 9 24 5 1 2 8 10 I have tried sum = apply(ages,1,add) but it gives me a row vector. Can some one please show me an efficient command to sum and product and append them to original data frame as shown above? 回答1: Try transform(df, sum=rowSums(df), prod=x*y*z) # x y z sum prod #1 1 2 3 6 6 #2 2 3

calculate row sum and product in data.frame

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Vectorize() vs apply()

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问题 The Vectorize() and the apply() functions in R can often be used to accomplish the same goal. I usually prefer vectorizing a function for readability reasons, because the main calling function is related to the task at hand while sapply is not. It is also useful to Vectorize() when I am going to be using that vectorized function multiple times in my R code. For instance: a <- 100 b <- 200 c <- 300 varnames <- c('a', 'b', 'c') getv <- Vectorize(get) getv(varnames) vs sapply(varnames, get)

$apply in setTimeout

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问题 I konw that $apply used to connect the Javascript context and the AngularJS context. A simple example is below: template: <div>{{someVal}}</div> javascript in controller: setTimeout(function() { scope.$apply(function(){scope.someVal = 123}); }, 1000); We need use $apply in above situation. First Qustion: If I modify javascript above to: setTimeout(function() { scope.someVal = 123; }, 1000); scope.$watch('someVal', function(val) { console.info(someVal); }); No console about someVal modified to

R: apply a function to a list of dataframes and save to workspace

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问题 I have a lot of tibbles similar to this one: dftest_tw <- structure(list(text = c("RT @BitMEXdotcom: A new high: US$500M turnover in the last 24 hours, over 80% of it on $XBTUSD. Congrats to the team and thank you to our u…", "RT @Crowd_indicator: Thank you for this nice video, @Nicholas_Merten", "RT @Crowd_indicator: Review of #Cindicator by DataDash: t.co/D0da3u5y3V" ), Tweet.id = c("896858423521837057", "896858275689398272", "896858135314538497" ), created.date = structure(c(17391, 17391,

前端基础回顾之手写题

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前言本文还是依然针对前端重点基础知识点进行整体回顾系列的一篇，目标是帮助自己理解避免死记硬背。下面针对new、Object.create、call、apply、new、bind 等基础API，从用法到原理实现过一遍，期望看完之后大家实现时不是死记硬背而是根据理解记忆推导。基础准备在探究上述内容原理之前，可以将上述API分为两类。一类是new、Object.create这两者，涉及实例化对象的。其对应的基础内容部分和上篇前端面试基础回顾之深入JS继承的基础部分相同。就是原型链和构造函数，这里不再赘述。剩下的就是关于this指向的修改。这里我们可以看下 MDN中对this的描述。 this由调用时环境确定，简单总结如下：显式指定： new 实例化 this指向新构建的对象(new 显式返回一个对象，则this指向该返回对象，否则指向该对象实例) // 例如 var bar = new foo() bind、call、apply ，指向绑定对象 var bar = foo.call( obj2 ) 隐式指定：函数作为对象属性调用，即如object.func()形式，指向该对象。 //指向obj1 obj1.foo() 无指定即不属于以上情况，为默认绑定。在strict mode下，就是undefined，否则是global对象。 var fun1 =

How do I apply unknown arguments to a function in Python 3.x?

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问题 I'm developing my own GUI for my engine, and I've created an "object" called EwConsole (A simple "drop-down" console to input commands). In order to do that, I simply store an ID for the function to be "triggered with enter/return" as the key to the function-object itself in a dict. My problem is with the arguments, and Python 3.x. Here's my method for creating a new "console command": def create_command(self, command_id, command_function): self["commands"][command_id] = command_function I've

how to run chisq.test in loops using apply

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问题 I am a newbie of R. Due to the need of my project, I need to do Chisq test for hundred thousand entries. I learned by myself for a few days and write some code for runing chisq.test in loops. codes: the.data = read.table ("test_chisq_allelefrq.txt", header=T, sep="\t",row.names=1) p=c() ID=c() for (i in 1:nrow(the.data)) { data.row = the.data [i,] data.matrix = matrix ( c(data.row$cohort_1_AA, data.row$cohort_1_AB, data.row$cohort_1_BB, data.row$cohort_2_AA, data.row$cohort_2_AB, data.row

R - Create a ordered list from a matrix

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问题 Hi there! I have this 24x24 matrix with a lot of numbers from 1-24. Where I want to turn every cell with the value of X (eg. 3) into the row.name of the X'th row (eg. name3) What I have row.names V1 V2 V3 name1 1 3 10 name2 3 20 1 name3 5 13 2 ... .. .. .. name24 19 3 4 What I want to do now, is turn all these numbers into a character string equvivalent to the i'th row name so a 1 should be converted to name1 and so forth. What I need row.names V1 V2 V3 name1 name1 name3 name10 name2 name3

apply a function to a groupby function

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问题 I want to count how many consistent increase, and the difference between the first element and the last element, on a groupby. But I can't apply the function on the groupby. After groupby, is it a list? And also what's the difference between "apply" and "agg"? Sorry, I just touched the python for a few days. def promotion(ls): pro =0 if len(ls)>1: for j in range(1,len(ls)): if ls[j]>ls[j-1]: pro + = 1 return pro def growth(ls): head= ls[0] tail= ls[len(ls)-1] gro= tail-head return gro