CODEWITHSUNDEEP
r
John
John

Reputation: 1947

Creating vectors with respect to remainder

I have the problem following : Let's say we consider numbers from 1 to 102. I want to create four vectors a,b,c,d in such way :

Vector a takes value 1 if a=4k+1 and 0 otherwise

Vector b takes value 1 if a=4k+2 and 0 otherwise

Vector c takes value 1 if a=4k+3 and 0 otherwise

Vector d takes value 1 if a=4k and 0 otherwise

for some integer k.

My work so far

a<-b<-c<-d<-c()
for (i in 1:102)){
  if (i%%4==1){a[i]<-1}
  else (a[i]<-0)
}
for (i in 1:102){
  if (i%%4==2){b[i]<-1}
  else (b[i]<-0)
}    
for (i in 1:102){
  if (i%%4==3){c[i]<-1}
  else (c[i]<-0)
}
for (i in 1:102){
  if (i%%4==0){d[i]<-1}
  else (d[i]<-0)} 
}

Question

Is there any faster way to do that without using 4 loops ?

Upvotes: 0

Views: 37

Answers (1)

Gregor Thomas
Gregor Thomas

Reputation: 145965

%% is vectorized, so you don't need any loops. And ifelse is a vectorized version of if(){}else{}.

rem = 1:102 %% 4
a = ifelse(rem == 1, 1, 0)
b = ifelse(rem == 2, 1, 0)
c = ifelse(rem == 3, 1, 0)
d = ifelse(rem == 0, 1, 0)

The ifelse makes it clear that you are getting a 1 or 0 output, but you can also do, e.g., a = as.integer(rem == 1) to coerce the TRUE/FALSE directly to 1 and 0 instead of using ifelse. It's a little more efficient, though perhaps a little less clear.

Upvotes: 4

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