R：根据数据计数生成直方图

Question

Suppose I have vector a :

c(1, 6, 2, 4.1, 1, 2)

And a count vector b :

c(2,3,2,1,1,0)

I'd like to generate vector c :

c(1, 1, 6, 6, 6, 2, 2, 4.1, 1)

To call:

hist(c)

How can I build c , or is there a way to generate the histogram directly from a and b ? Note the duplicates in a , as well as unequal spacing.

Require a vectorized solution. a and b are too large for lapply and friends.

Answer 1

?rep

> rep(a, b)
[1] 1.0 1.0 6.0 6.0 6.0 2.0 2.0 4.1 1.0
> 

---

Edit since I was curious!

a <- sample(1:10, 1e6, replace=TRUE)
b <- sample(1:10, 1e6, replace=TRUE)

> system.time(rep(a, b))
   user  system elapsed 
  0.140   0.016   0.156 
> system.time(inverse.rle(list(lengths=b, values=a)))
   user  system elapsed 
  0.024   0.004   0.028 

Answer 2

Just for something different than rep :

> inverse.rle(list(lengths=b,values=a))
[1] 1.0 1.0 6.0 6.0 6.0 2.0 2.0 4.1 1.0

Answer 3

Some benchmarking and a faster solution. rep.int is a faster implementation of rep in the standard use case (from ?rep )

rep.int(a, b)

I wasn't convinced on the benchmarking above

inverse.rle is just a wrapper for rep.int . rep.int should be faster than rep . I would think that the wrapper component of inverse.rle should be slower than the interpretation of rep() as a primitive function

Some microbenchmarking

library(microbenchmark)

microbenchmark(rep(a,b), rep.int(a,b), 
      inverse.rle(list(values = a, lengths =b)))
Unit: milliseconds
                                        expr      min       lq   median       uq
1 inverse.rle(list(values = a, lengths = b)) 29.06968 29.26267 29.36191 29.67501
2                                  rep(a, b) 25.65125 25.76246 25.84869 26.52348
3                              rep.int(a, b) 20.38604 23.31840 23.38940 23.69600
       max
1 72.80645
2 69.00169
3 66.40759

There isn't much in it, but rep.int appears the winner - which it should.