coursera R Programming NOTE(6)

1348 단어

loop functions

lapply(list,function) example: 
x
sapply(list,function) The sapply() function behaves similarly to lapply()
  • If the result is a list where every element is length 1, then a vector is returned
  • If the result is a list where every element is a vector of the same length (> 1), a matrix is returned.
  • If it can’t figure things out, a list is returned
    • tapply(vector,INDEX,function)
  • INDEX is a factor or a list of factors (or else they are coerced to factors) example: 
    • x
    apply(array,dims,function) example: 
     x

    Col/RowSumsandMeans 
    rowSums = apply(x, 1, sum)
rowMeans = apply(x, 1, mean)
colSums = apply(x, 2, sum)
colMeans = apply(x, 2, mean)
    mapply(function,argument1,argument2,argument3...) example: 
    mapply(rep, 1:4, 4:1)
## "1:4" is the first argument of function "rep"
## "4:1" is the second argument of function "rep"

noise
    split(vector or list or data frame,factor) The split() function takes a vector or other objects and split sitin to groups determined by a factor or list of factors. example: 
     x
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