For Loop performance

v1[1] with v2[1] and v2[2] and v1[2] with v2[3] and v2[4]
or
v1[1] with v2[1] and v2[n+1] and v1[2] with v2[2] and v2[n+2]

My Coyne wrote:

Hello,



Newbie question and hope you can help .

I have two vector V1 and V2, where length(V2) = length of (V1) * 2;
length(V1) ~ 16,000.

For each member in V1, I need to compare 2 element of V2 for equality

If just the comparison is concerned, you can do it in vectorized form,
but I am not sure of you want to comapre v1[i] with v2[i] and v2[i+1],
otherwise it would not make sense that  length(V2) = length of (V1) * 2
...

Say length(V1) is n, do you want to compare

v1[1] with v2[1] and v2[2] and v1[2] with v2[3] and v2[4]
or
v1[1] with v2[1] and v2[n+1] and v1[2] with v2[2] and v2[n+2]

???

Uwe Ligges

i.e.

for (I in 1:length (V1)) {

     if ( v2[i] == v1[i] & v2[i+1]==v1[i] ){

          statement_1

          statement_2

          .

     }

}



This for-loop is too slow (it takes a good 5 minutes on my Windows
machine)
to  finish processing the vector V1 of 16,000; I will need to process a
lot
more than 16,000  (about 300*16,000).



Is there a better way to do looping with R?  Any help is greatly
appreciate



--MyC.
















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