7. The na_example vector represents a series of counts. You can quickly examine the object using:

library(dslabs)
data("na_example")  
str(na_example)
#>  int [1:1000] 2 1 3 2 1 3 1 4 3 2 ...

However, when we compute the average with the function mean, we obtain an NA:

mean(na_example)
#> [1] NA

The is.na function returns a logical vector that tells us which entries are NA. Assign this logical vector to an object called ind and determine how many NAs does na_example have. Store your anwser in na_count.

Hint: you can use the sum function to count the number of occurences of TRUE in a logical vector. The TRUE values will be counted as 1 and the FALSE values as 0.

8. Now compute the average again, but only for the entries that are not NA. Store the average in vector_mean.

Hint: you can subset a vector using a logical vector as index vector[logical].

Hint: remember the ! operator.