Some R Functions

apply chartr lapply nchar paste readLines substr trimws

apply

Description: Return a vector or array or list of values obtained by applying a function to margins of an array or matrix.
Required Parameters:
        x -- matrix or array
        margin -- vector of dimensions over which the function will be applied. For a matrix, 1 = apply over rows, 2 = apply over columns.
          function -- function to apply to margins of a matrix or array
Return Value: A vector or matrix of the function applied to the specified margins.

m <- matrix(c(1:10, 11:20, 10:1), nrow = 5, ncol = 3)
m
# Output:
    [,1] [,2] [,3]
[1,]  1    6   11
[2,]  2    7   12
[3,]  3    8   13
[4,]  4    9   14
[5,]  5   10   15

# Find medians of rows
apply(m, 1, median)
# Output:
[1] 6 7 8 9 10

# Find means of columns
apply(m, 2, mean)
# Output:
[1] 3  8 13

chartr

Description: Perform character translations (string substitutions) in strings.
Required Parameters:
     old -- existing characters to translate
     new -- new characters to use for translation
         x -- input string to translate
Return Value: Character vector of translated strings.

Example:

chartr("acg", "hdb", "class assignment")
# Output:
[1] "dlhss hssibnemnt"

v <- c("class", "assignment")
chartr("acg", "hdb", v)
# Output:
[1] "dlhss"  "hssibnemnt"

lapply

Description: Apply a function to the components of a list.
Required Parameters:
x -- A list.
function -- Function to be applied to the components of the list.
Return Value: List with the return values of the function applied to the list components.

Example:

lst <- list(a=c(1, 2), b=c(3, 4, 5))
lapply(lst, sum)
# Output:
$a
[1] 3

$b
[1] 12

nchar

Description: Return the lengths of strings in a character vector.
Required Parameter: x -- A character vector.
Return Value: A numeric vector containing the lengths of the strings in the input vector.

Example:

v <- c("one", "two", "three", "four")
nchar(v)
# Output:
[1] 3 3 5 4

paste

Description: Takes any number of input arguments and concatenates them together componentwise
Required Parameters: Items to concatenate of any mode
Optional Parameters: sep -- The separator item to be inserted between concatenated items
Return Value: A character vector of concatenated items.

Example:

a <- c(1,2,3)
b <- c("a","b","c")
paste(a, b, sep=";")
# Output:
[1] "1 a" "2 b" "3 c"

paste(a, b, sep=";")
# Output:
[1] "1;a" "2;b" "3;c"

paste(a, b, sep="")
# Output:
[1] "1a" "2b" "3c"

readLines

Description: Read some or all text lines from a defined connection (for example a file).
Required Parameters: con -- the connection string.
Return Value: A character vector that contains the lines of the file.
Important Optional Parameters: n -- maximum number of lines to read, negative means read the entire file, default = -1.
Examples:
Note: If the connection is to a file, the filename can be used instead of the connection object:
If the filename is used in the readLines function, reading always starts at the beginning of the file, whereas with a connection object, reading resumes with the next line after the last line that was read on the previous call to readLines. Close each connection object after you are finished reading from it.

strsplit

Description: Split strings in a character vector into a list of character vectors.
Required Parameters:
x -- character vector
split -- delimiters to use for splitting
Return Value: A list of the strings in x split into vectors

Example:

v <- c("apple,elephant,student")
strsplit(v, ",")
# Output:
[[1]]
[1] "apple" "elephant" "student" 

w <- c("apple,elephant,student", "abc;xyx")
strsplit(v, c(",", ";"))
# Output:
[[1]]
[1] "apple" "elephant" "student" 

[[2]]
[1] "abc" "xyx"

substr

Description: Return substrings of the strings in a character vector.
Required Parameters:
     x -- character vector
     start -- positions of start of substrings to extract or replace
     stop -- positions of end of substrings
         These parameters are recycled as needed.
Return Value: A character vector of extracted substrings.

Example:

substr("abcdefg", 3, 5)
# Output:
[1] "cde"

v <- c("abcdefg", "mnopqrst", "wxyz")
substr(v, 3, 5)
# Output:
[1] "cde" "opq" "yz" 

substr(v, 1:3, 2:4)
# Output:
[1] "ab" "no" "yz"

trimws

Description: Trim whitespace from the beginning and/or end of a strings in a character vector.
Required Parameter: x -- A character vector.
Optional Parameter: which -- Indicates where to trim whitespace.
Values are "both" (default): trim leading and trailing whitespace, "left": trim whitespace only on left, "right": trim whitespace only on right.
Return Value: A character vector with whitespace trimmed.

Example:

v <- c(" abc  ", " cde ", " xyz ")
trimws(v, which="both") 
# Output:
[1] "abc" "cde" "xyz"

trimws(str, which="left")
# Output:
[1] "abc  " "cde " "xyz " 

trimws(str, which="right")
# Output:
[1] " abc" " cde" " xyz"