r-commands - Math 127B Basic R R commands Mrinal Raghupathi...

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Math 127B, Basic R, R commands Mrinal Raghupathi This is a list of the commands we use most often in R. The list is not comprehensive, but it covers most of the things we need. 1 Making lists, data frames Basic list creation Make a list and assign it to a name x <- c(1,2,3) Sequence seq(start, stop, step) creates the list of numbers beginning at start, in steps of size step until it reaches stop . > x <- seq (3 ,15 ,4) > x [1] 3 7 11 15 Repetition rep(number, times) produces a list with number repeated times times. > x <- rep (5 ,7) > x [1] 5 5 5 5 5 5 5 Dollar The $ sign can be used to extract a properties. For example the value returned from the lm command, or the column of a data frame. Data frame data.frame() can be used to make a data frame. Supply the names of the columns and the corresponding values with options of the form name = value . > men <- c(45, 86, 12) > women <- c(30 ,105 ,21) > both <- data.frame(gents = men , ladies = women) > both gents ladies 1 45 30 2 86 105 3 12 21 > both$ladies [1] 30 105 21 You can assign a list as a new column of the data frame by using the $ operation and assigning the list to it. 1
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2 Statistics Frequency tables table(x) produces the frequencies for entries in x . > grades <- c(’a’, ’b’, ’a’, ’b’,’a’,’a’,’a’,’a’,’b’) > length(grades) [1] 9 > table(grades) x a b 6 3 Using two lists you can get the cross tabulation. For example here are the subject areas in which the grades were recieved. > subjects <- c(’math ’, ’math ’, ’physics ’, ’physics ’ ,’math ’, ’math ’, ’physics ’, ’physics ’, ’math ’) > table(subjects) subjects math physics 5 4 > table(grades , subject) subject grades math physics a 3 3 b 2 1 Correlation cor(x,y)
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