CODEWITHSUNDEEP
rsyntax
Andrew
Andrew

Reputation: 7545

In R, how does double percent work when used on a matrix?

    a <- data.frame(1:50)
    a %% 10==0

It returns TRUE for row numbers in increments of 10, starting at 0.

    a %% 10==2

This does the same thing, but starting at 2.

How does this syntax work? I know what %% is as an operator but I don't understand what's happening in this scenario.

Upvotes: 2

Views: 459

Answers (1)

Liesel
Liesel

Reputation: 2979

(Hope I haven't over explained this and interpreted what you're asking correctly:)

As you've said, you know that %% is the modulus operator. So

a <- data.frame(1:50)
a %% 10

returns 'x mod 10' for each item in the frame (or 1,2,3,4,5,6,7,8,9,0 etc etc)

The two examples you've given are like 'shorthand' for if statements. In pseudo code:

for n = 1 to length of a
    if a[n] %% 10 equals zero 
      return true
    else 
      return false

So a %% 10 == 0 is "Does the element mod 10 equal zero" and a %% 10 == 2 is "Does the element mod 10 equal two" applied to each element

And the result is matrix of logicals (booleans).

Upvotes: 2

Related Questions