-Exercise

Sometimes you want to select elements from a vector in a more advanced fashion. This is where the use of logical operators may come in handy.

The (logical) comparison operators known to R are:

- < for less than

- > for greater than

- <= for less than or equal to

- >= for greater than or equal to

- == for equal to each other全相等

- != not equal to each other不全相等

The nice thing about R is that you can use these comparison operators on vectors. For example, the statement c(4,5,6) > 5 returns: FALSE FALSE TRUE. In other words, you test for every element of the vector if the condition stated by the  comparison operator is TRUE or FALSE.

Behind the scenes, R does an element-wise  comparison  of  each  element    in   the vector  c(4,5,6)  with  the  element  5.  However,  5 is not a  vector of  lengththree. To solve this, R automatically replicates the value 5 to generate a vector of three elements, c(5, 5, 5) and then carries out the element-wise comparison.只要两组向量长度一样就可以做比较 如果长度不一样 

instructions

• Check which values in numeric_vector are larger than 10. Assign the result to  the variable larger_than_ten.

• print the variable larger_than_ten to the console.

注意辨析

numeric_vector <- c(1, 10, 49)

> numeric_vector==c(1,10,49)

[1] TRUE TRUE TRUE

> numeric_vector!=c(1,10,49)

[1] FALSE FALSE FALSE

> numeric_vector<=c(2,11)

[1]  TRUE  TRUE FALSE

Warning message:In numeric_vector <= c(2, 11) : longer object length is not a multiple of shorter object length

> numeric_vector==c(1,11,49)

[1]  TRUE FALSE  TRUE

> numeric_vector!=10

[1]  TRUE FALSE  TRUE