Question

I’ve got a data frame that represents points in a plane.

     x     y
1  0.0   0.0
2  0.2   0.0
3  0.3  -0.1
...

I want to write a diff-like function for that data. I’ve written the distance function myDist (not Euclidean), but how can I apply it to the data frame?

That is: By calling someFunction( myData, myDist ), I want to obtain a vector with the values myDist(myData[1,],myData[2,]), myDist(myData[2,],myData[3,]), myDist(myData[3,],myData[4,]), …

Is there a function that does this, or do I have to write a loop?

Answer 1

Solved it with lapply:

lapply(seq_len(nrow(myData) - 1),
    function(i){
        myDist( myData[i,], myData[i+1,] )
    })