What is the difference between [ ] and [[ ]] in R? -

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this question has answer here:

  > levels(state.region)[2]     [1] "s"     > levels(state.region)[[2]]     [1] "s"

they return same value, don't know difference between them.

[] = returns object of same class (out of basic object classes), can select more 1 element of object

[[]] = can extract 1 element list or data frame, returned object (out of basic object classes) not list/dataframe


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