Page 224 - Data Science class 11
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b.  using logical indexing ( starts with -1,-2 from left hand side)
        Indexing is used in order to access the elements in a vector. The [] brackets are used for indexing. Indexing starts with
        position 1. Providing a negative value in the index drops the element from the result. You can also use TRUE/FALSE
        or 0 and 1 for indexing.
        Example
        Enter the following code snippet:

             #Accessing vector elements using logical indexing.
             t <- c("Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul")
             v<- t[c(TRUE,FALSE,TRUE, FALSE, FALSE, TRUE, TRUE)]
             print(v)
        The following result is produced:

















        c.  using negative indexing indexing (starts with -1,-2 from left hand side)
        Example

        Enter the following code snippet:

             #Accessing vector elements using negative indexing.
             z <- c("first", "second", "third", "fourth", "fifth", "sixth", "seventh")
             x <- z[c(-1,-4)]
             print(x)
        The following result is produced (here it drops the elements at the index -1 and -4):
















        d.  using 0/1 indexing
         Example
        Enter the following code snippet:

             #Accessing vector elements using 0/1 indexing.
             z <- c("first", "second", "third", "fourth", "fifth", "sixth", "seventh")
             y<- z[c(1,0,0,1,0,0,1)]
             print(y)


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