I am developing a function and I find it hard to boil down to MWE. But the weird thing is the function runs in about 13 seconds, so I try to `@time`

various part of the program and the code runs in 2 seconds.

There is nothing different about the code except I have placed `@time`

at 2 places. See

```
Pkg.clone("https://github.com/xiaodaigh/FastGroupBy.jl")
using FastGroupBy
byveccv = (rand(1:100,10_000_000), rand(1:100, 10_000_000))
val = rand(1:5,10_000_000)
@time FastGroupBy.fgroupreduce!(+, byveccv, val, 0) # 2 seconds
@time FastGroupBy.fgroupreduce2!(+, byveccv, val, 0) # 13 seconds
```

and here is the code for the two functions

```
function fgroupreduce!(fn::F, byveccv::Tuple, val::Vector{Z}, v0::T = zero(T)) where {F<:Function, Z, T}
l = length(val)
index = collect(1:l)
lb = length(byveccv)
grouptwo!(byveccv[lb], index)
@inbounds val .= val[index]
@time @inbounds for i = lb-1:-1:1
byveccv[i] .= byveccv[i][index]
end
@time @inbounds for i = lb-1:-1:1
index .= collect(1:l)
grouptwo!(byveccv[i], index)
for j = lb:-1:i+1
byveccv[j] .= byveccv[j][index]
end
val .= val[index]
end
diff2prev = da(byveccv)
n_uniques = sum(diff2prev)
upto::UInt = 0
res = fill(v0, n_uniques)
res[1] = v0
resby = ((bv[diff2prev] for bv in byveccv)...)
@inbounds for (vali, dp) in zip(val, diff2prev)
# increase upto by 1 if it's different to previous value
upto += UInt(dp)
res[upto] = fn(res[upto], vali)
end
(resby..., res)
end
function fgroupreduce2!(fn::F, byveccv::Tuple, val::Vector{Z}, v0::T = zero(T)) where {F<:Function, Z, T}
l = length(val)
index = collect(1:l)
lb = length(byveccv)
grouptwo!(byveccv[lb], index)
@inbounds val .= val[index]
@inbounds for i = lb-1:-1:1
byveccv[i] .= byveccv[i][index]
end
@inbounds for i = lb-1:-1:1
index .= collect(1:l)
grouptwo!(byveccv[i], index)
for j = lb:-1:i+1
byveccv[j] .= byveccv[j][index]
end
val .= val[index]
end
diff2prev = da(byveccv)
n_uniques = sum(diff2prev)
upto::UInt = 0
res = fill(v0, n_uniques)
res[1] = v0
resby = ((bv[diff2prev] for bv in byveccv)...)
@inbounds for (vali, dp) in zip(val, diff2prev)
# increase upto by 1 if it's different to previous value
upto += UInt(dp)
res[upto] = fn(res[upto], vali)
end
(resby..., res)
end
```