[Nicola Tommasi]

reshape long cusip@ base@, i(DealNumber) j(id_alliance)
drop if cusip==""
replace match=cusip if match=="" & base==1

[Nicola Tommasi]

Reshape is best solution, this one is only a "joke" whitout reshaping data
In your real data replace forvalues s=1/10
with forvalues s=1/20

expand sum
sort DealNumber
bysort DealNumber: gen id_deal = _n

levelsof DealNumber if match=="", local(deals)

foreach i of local deals {
  local sequence ""
  forvalues s=1/10 {
    count if base`s'==1 & DealNumber=="`i'"
    if r(N)>0 local sequence = "`sequence' `s'"
  }

  local cnt=1
  di "DealNumber `i', sequence `sequence'"
  foreach d of local sequence {
    replace match=cusip`d' if DealNumber=="`i'" & base`d'==1 & id_deal==`cnt'
    local cnt `++cnt'
  }
}

[killian mccarthy]

Nick, Fantastic. I was making it too complex. This is a much neater solution. Thanks! Killian