lapply

The R language provides a bulk processing function that iterates through all or part of the elements within a collection to simplify operations. The bottom of these functions is achieved by C, so efficiency is more efficient than manual.The batch processing function has very important apply family function: lapply sapply apply tapply mapply. The Apply family function is one of the methods to realize the computational quantization (vectorization) with

), Usena = C ("No", "Ifany", "Always"), DNN = List.names (...), Deparse. Level = 1) where the parameter exclude indicates which factors are not counted.Example code:> D > D[1] A b c A b c a b c a b c a b c a b c a b c a b c a b c a B CLevels:a B C D E> table (d)DA B C D E10 10 10) 0 0> table (d, exclude= "B")DA C D E10 10 0 0 function lapply and function sapply: Lapply is used in the following

a factor when necessary. Example code: > FAC $ ' 2 ' [1] 57 $ ' 3 ' [1] 45 $ ' 4 ' NULL $ ' 5 ' NULL > Tapply (1:17, FAC, RANGE) $ ' 1 ' [1] 1 16 $ ' 2 ' [1] 2 17 $ ' 3 ' [1] 3 15 $ ' 4 ' NULL $ ' 5 ' NULL #利用tapply实现类似于excel里的数据透视表的功能: > da year Province Sale 12007 Nbsp;a1 22007 b2 32007c 3 42007d 4 52008a5 6 2008c6 72008 d7 82009 b8 92009 c9 2009d10 > attAch (DA) > Tapply (sale,list (year,province)) [1]147 102 8 1169 > Tapply (sale,list (year,province), mean) ab cd 200712 34 20085 NA 6 7 na

Apply ()Apply (M,dimcode,f,fargs) M is a matrix. DimCode is the dimension number, 1 is applied to the row, and 2 is the function for the column. F is a function Fargs is an optional parameter set for F > z > f + x/c(2, 8)+ }> apply(z,1,f) #f函数得到两个元素，则为几行，竖着来的 [,1] [,2] [,3][1,] 0.5 1.000 1.50[2,] 0.5 0.625 0.75Lapply ()Lapply () (on behalf of list apply) is similar to the use of the Apply () function of the matrix, ex

Apply ()Apply (M,dimcode,f,fargs) M is a matrix. DimCode is the dimension number, 1 is applied to the row, and 2 is the function for the column. F is a function Fargs is an optional parameter set for F > z > f + x/c(2, 8)+ }> apply(z,1,f) #f函数得到两个元素，则为几行，竖着来的 [,1] [,2] [,3][1,] 0.5 1.000 1.50[2,] 0.5 0.625 0.75Lapply ()Lapply () (on behalf of list apply) is similar to the use of the Apply () function of the matrix, ex

More busy than busy more recently ... Really busy///As a rookie, do not understand why so easy to forget the basic operation of R, feel more difficult than C # JAVA, and to review again1 ##数据操作的入门2 3 ##定义一个函数判断偶数4Func function (x)5 {6 if(x% 2 = =0)

ObjectiveAt the beginning of the contact with the R language, you will hear a variety of R language use skills, the most important one is not to use the loop, the efficiency is particularly low, to use vector computing instead of cyclic calculation.So, what is this for? The reason is that R's cyclic operation for and while, are based on the R language itself, and the vector operation is based on the underlying C language function implementation, from the performance point of view, there will be

Looping on the Command lineWriting for, while loops was useful when programming and not particularly easy when working interactively on the command Li Ne. There is some functions which implement looping to make life easierlapply: Loop over a list and evaluate a function on each elementsapply: Same as Lapply but try to Simpli FY the resultApply: Apply a function over the margins of an arraytapply: Apply a function over subsets of a vector mapply:multiv

I. Apply family functions1.apply applied to matrices and arrays# apply # 1 for row, 2 for column # Create a matrix of ten rows x 2 columnsm 2.eapply variables applied to the environment# a new Environmente 3.lapply applies to the list, returns the list, and the actual data.frame is also a list, a list:lapply (list, function) cbind together by multiple vectors of the same lengthSapply (Iris[,1:4],mean) sepal.length sepal.width petal.length petal.width

Apply Apply Functions over Array MarginsUse functions against column rows or columns Apply (X, MARGIN, fun, ...) Lapply Apply a Function over a List or VectorUsing functions on lists or vectors Lapply (X, fun, ...) Sapply Apply a Function over a List or VectorUsing functions on lists or vectors Sapply (X, fun, ..., simplify = TRUE, use.) NAMES = TRUE)

There are several commonly used functions in the R language, which can be processed by group, apply, Lapply, sapply, tapply, mapply, etc. These functions are somewhat similar, and the following describes the usage of these functions.ApplyThis is an operation on a matrix or array for a dimension. The format is: Apply (data, dimension index, arithmetic function, function parameter) For the matrix, the dimension value is 2, the second parameter dimension

A) server-side code demo1) Constant definition:Const ' Department '; ' Employees '; 2) query data:function TServerMethods1.Getdepartmentemployees(Const AID:String): Tfdjsondatasets;BeginClear active So, query would reexecute. Fdquerydepartmentemployees.Active:=False; Fdquerydepartment.Active:=False; Fdquerydepartment.Params[0].Value:= AID; Fdquerydepartmentemployees.Params[0].value := aid; // Create DataSet list Result := tfdjsondatasets. Create//ADD departments DataSet Tfdjsondatasetswriter

index: Note the following code:#提取列表组件三种方法j1 　　To add or remove a list element:Add list elements: Use the index directly to increase the list components, there are 5 ways to see the code above, you can add a single component, or you can add a sub-list as a list of multiple components.Delete List element: Assigns the component to be deleted directly to NULL. Note that when you delete an intermediate component, the index of the subsequent component is all minus 1Get list Length:The length () func

);Result: = tfdjsondatasets. Create;Tfdjsondatasetswriter. listadd (result, D. qry );ExceptOn E: exception doBeginResult: = nil;Log. writelog ('tservermethods1. querysql2 '+ E. Message );End;End;FinallyDbpool. Unlock (d );End;EndElseResult: = nil;End; Function tservermethods1.savedata (const tablename: string;Delta: olevariant): Boolean;VaRD: tfrmdb;Errcnt: integer;BeginD: = dbpool. lock;If assigned (d) thenBeginTryTryD. qry. close;D. qry. SQL. Clear;D. qry. SQL. Text: = 'select * from' + table

cachemean execution? Getmean#This copies the M to Getmean (NULL)List (set=set,get=GET, Setmean=Setmean, Getmean=Getmean)} Cachemeanfunction (x, ...) {m#first assign the Getmean to M, and if M is not NULL, the following hint pops up if(! is. Null (M)) {Message ("Getting cached data") return(M)}#Cache value appearsData#assigns the first numberic vector to the datammean (data, ...) X$setmean (m) cache M-m}AboveIn addition, several useful functions were also discussed this wee

columns of the matrix: look for an example of changing the size of a matrix 613.4.2 by adding or deleting a matrix row or column 613.4.1 with an abnormal value 603.4: find the difference between the closest 633.5 vector and the matrix of an endpoint in the graph. 653.6 avoid unexpected dimensionality reduction. 663.7 naming of rows and columns of the 683.8 matrix. 4th high-dimensional array. 68 chapter 714.1 list. 714.2 create list general Operation 724.2.1 List Index 724.2.2 add or delete list

repeated calculation results In the simplest condition group, the condition does not overlap, but in fact it is very common to overlap. For example, grouping order amounts according to the following rules: 1000 to 4000: regular order R14 Less than 2000: Non-key order r2 More than 3000: Key orders r3 The regular orders here will overlap with the other two groups. In this case, whether or not to repeat the overlapped data is required. Code: R14 R2 R3 Grouped Result Calculation Result: 650) T

()Filtering subsets: sel|, ,! =, = =Order ()Merge ()As.factor (); As.numeric (); As.character ();Factor (Squid$sex, Levels=c), Labels=c ("M", "F"))Tapply (); Tapply (X=veg$r,index=veg$transect, Fun=mean) averages the first variable according to the different levels of the second variable;Mean,min,max,sd,length,Lapply () multiple variables; output list;lapply (X,fun=mean)Sapply () multiple variables; output

Recently participated in a small game where the tapply,sapply (lapply) function can quickly achieve my purpose and effectively reduce the amount of code F Description Tapply (X,F,G) X is a vector, F is a factor column, G is an action function, and a similar operation with a data frame can be done by using the by function Sapply (LIST,G) G is the operation function, the return result is a vector, an

operations at the same time, usually by executing the same or a batch of instructions on different data, or applying an instruction to an array/vector, compared to the way the general program performs only one operation at a time. The following list of several vectorization operations used frequently in R is a trivial operation, but they are essentially the same operations applied to a batch of data at the same time, so they can be transformed by a vectorization approach:Vector values, such as: