gistfile1.txt

I have a set of taxonomies and I want to return a consensus taxonomy masking the levels that aren't shared by all members, e.g. 
["Liliopsida;Poales;Poaceae;Elymus;Elymus repens", "Liliopsida;Poales;Poaceae;Elymus;Elymus nutans"] 
should produce "Liliopsida;Poales;Poaceae;Elymus;", 
but those plus "Liliopsida;Poales;Cyperaceae;Carex;Carex ovalis" should equal "Liliopsida;Poales;;;"

My first stab:

def mask_to_agreement(taxstrings):
    taxlists = [t.split(';') for t in taxstrings]
    taxout = [''] * len(taxlists[0]) # assumes all lists are same length!
    for i in range(0, len(taxlists[0])):
        taxon = taxlists[0][i]
        if [t[i] for t in taxlists].count(taxon) == len(taxlists):
            taxout[i] = taxon
        else:
            break
    return ';'.join(taxout)
    
This appears to works, but seems awfully baroque -- is there a way to do this as a common-substring operation instead?

def mask_to_agreement2(taxstrings):
    taxtuples = zip(*[t.split(';') for t in taxstrings])
    taxout = []
    for t in taxtuples:
        if t.count(t[0]) == len(t):
            taxout.append(t[0])
        else:
            taxout.append('')
    return ';'.join(taxout)

>>> a = "A;B;C;D;E"
>>> b = "A;B;C;D;F"
>>> c = "A;B;G;H;I"
>>> mask_to_agreement([a,b])
'A;B;C;D;'
>>> mask_to_agreement([a,b,c])
'A;B;;;'
>>> mask_to_agreement2([a,b])
'A;B;C;D;'
>>> mask_to_agreement2([a,b,c])
'A;B;;;'

a = "Liliopsida;Poales;Poaceae;Elymus;Elymus repens"
b = "Liliopsida;Poales;Poaceae;Elymus;Elymus nutans"
c = "Liliopsida;Poales;Cyperaceae;Carex;Carex ovalis"
d = "WRONG_Liliopsida;Poales;Cyperaceae;INVALID_Carex;Carex ovalis"

def common_head(hierarchies):
  hierarchies = [h.split(';') for h in hierarchies]
  common = hierarchies[0]
  for other in hierarchies[1:]:
    for level in range(len(common)):
      if other[level] != common[level]:
        common = common[:level]
        break
  return common

print(common_head([a, b]))
print(common_head([a, b, c]))
print(common_head([a, b, c, d]))
print(common_head([a, d]))
print(common_head([a, c]))

def mask_to_agreement(taxstrings):
    taxlists = [t.split(';') for t in taxstrings]
    taxout = [''] * len(taxlists[0]) # assumes all lists are same length!
    for i in range(0, len(taxlists[0])):
        taxon = taxlists[0][i]
        if [t[i] for t in taxlists].count(taxon) == len(taxlists):
            taxout[i] = taxon
        else:
            break
    return ';'.join(taxout)