Swapping array values with for and yield scala

I am trying to swap every pair of values in my array using for and yield and so far I am very unsuccessful. What I have tried is as follows:

val a = Array(1,2,3,4,5) //What I want is Array(2,1,4,3,5)
 
 for(i<-0 until (a.length-1,2),r<- Array(i+1,i)) yield r
 

The above given snippet returns the vector 2,1,4,3(and the 5 is omitted)

Can somebody point out what I am doing wrong here and how to get the correct reversal using for and yields?

Thanks

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