【860】R programming related knowledge

Ref: R 字符串

Ref: R语言遍历文件和批量输出文件

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setwd(dir)getwd()getwd returns an absolute filepath representing the current working directory of the R process; setwd(dir) is used to set the working directory to dir.

 

head(x, n)Returns the first or last parts of a vector, matrix, table, data frame or function. Since head() and tail() are generic functions, they may also have been extended to other classes.

  This function is similar to df.head(n)in python.

nchar(x)It takes a character vector as an argument and returns a vector whose elements contain the sizes of the corresponding elements of x.

length(x)Get or set the length of vectors (including lists) and factors, and of any other R object for which a method has been defined.

  This function is similar to len(x)in python.

toupper()/tolower()

substring(x, start, stop)Extract or replace substrings in a character vector.

paste(..., sep = " ", collapse = NULL, recycle0 = FALSE)Concatenate vectors after converting to character.

paste0(..., collapse = NULL, recycle0 = FALSE)The sepis set with nothing by default.

ls()Return a vector of variables. rm()Remove the specific variable.

c()It is used to create a list to a vector.

R Lists

append(x, values, after = length(x))Add elements to a vector. The value will not add to xdirectly.

> a = list()
> for (i in c(1:10)) {a = append(a, i)}

R Data Frames

R Plotting

grep, grepl, regexpr, gregexpr, regexec and gregexec search for matches to argument pattern within each element of a character vector: they differ in the format of and amount of detail in the results.

 

 

 

list.files(path = ".", pattern = NULL, all.files = FALSE,
           full.names = FALSE, recursive = FALSE,
           ignore.case = FALSE, include.dirs = FALSE, no.. = FALSE)It produces a character vector of the names of files or directories in the named directory.

list.dirs()

If wanting to batch files, forloop can be used as follows,

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for   (i   in 1:  length  (files)) {     file =   read.table  (files[i], sep=  '\t' )   }