In R, what does a negative index do?



I am porting part of a program (not enough to compile and run) from R to C++. I am not familiar with R. I have done okay using the references online, but was stumped by the following line:


I am guessing:

  1. cnt2 is a 2 dimensional matrix
  2. cnt2.2 is a new variable being declared with a period '.' used the same way an alphabetic character would be.
  3. <- is an assignment.
  4. [,-1] accesses part of the array. I thought [,5] meant all rows, 5th column only. If this is correct, I have no idea what -1 refers to.

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