R | Data Selection and Manipulation

This functions below aim to give a bit of background on data and data manipulation in R.

  • which.max(x) returns the index of the greatest element of x
  • which.min(x) returns the index of the smallest element of x
  • rev(x) reverses the elements of x
  • sort(x) sorts the elements of x in increasing order; to sort in decreasing order: rev(sort(x))
  • cut(x,breaks) divides x into intervals (factors); breaks is the number of cut intervals or a vector of cut points
  • match(x, y) returns a vector of the same length than x with the elements of x which are in y (NA otherwise)
  • which(x == a) returns a vector of the indices of x if the comparison operation is true (TRUE), in this example the values of i for which x[i] == a (the argument of this function must be a variable of mode logical)
  • choose(n, k) computes the combinations of k events among n repetitions = n!/[(n−k)!k!]
  • na.omit(x) suppresses the observations with missing data (NA) (suppresses the corresponding line if x is a matrix or a data frame)
  • na.fail(x) returns an error message if x contains at least one NA
  • unique(x) if x is a vector or a data frame, returns a similar object but with the duplicate elements suppressed
  • table(x) returns a table with the numbers of the differents values of x (typically for integers or factors)
  • subset(x, …) returns a selection of x with respect to criteria (…,
  • typically comparisons: x$V1 < 10); if x is a data frame, the option
  • select gives the variables to be kept or dropped using a minus sign
  • sample(x, size) resample randomly and without replacement size elements in the vector x, the option replace = TRUE allows to resample with replacement
  • prop.table(x,margin=) table entries as fraction of marginal table


Functions for Manipulating Character Variables
nchar(x) a vector fo the lengths of each value in x
paste(a,b,sep=”_”) concatenates character values, using sep between them
substr(x,start,stop) extract characters from positions start to stop from x
strsplit(x,split) split each value of x into a list of strings using split as the delimiter
grep(pattern,x) return a vector of the elements of x that included pattern
grepl(pattern,x) returns a logical vector indicating whether each element of x contained pattern
regexpr(pattern,x) returns the integer positions of the first occurrence of pattern in each element of x
gsub(pattern,replacement,x) replaces each occurrence of pattern with occurrence
tolower(x) converts x to all lower case
toupper(x) converts x to all upper case


Logical Operators
== is equal to
!= is not equal to
> greater than
>= greater than or equal to
< less than
<= less than or equal to
%in% is in the list
! not (reverses T & F
& and
| or


ankara escort çankaya escort ankara escort çankaya escort ankara rus escort çankaya escort istanbul rus escort eryaman escort ankara escort kızılay escort istanbul escort ankara escort istanbul rus Escort atasehir Escort beylikduzu Escort