*To*: mathgroup@smc.vnet.net*Subject*: [mg10512] Re: [mg10480] ReplacePart?*From*: David Withoff <withoff@wolfram.com>*Date*: Tue, 20 Jan 1998 02:23:00 -0500

> I have a list of pairs of the form: > gt={{3,5},{{},6},{7,{}},{{},{}},{{},56},{{},3}}; > > The empty lists inside pairs are being used as placeholders. I want to > replace these with the elements of b: b={a1,a2,a3,a4,a5,a6}; > hopefully resulting in the list > {{3,5},{a1,6},{7,a2},{a3,a4},{a5,56},{a6,3}} > > I had thought that ReplacePart could do this, as it says: > "ReplacePart[expr, new, pos, npos] replaces parts at positions pos in > expr by > parts at positions npos in new." > > > I can't get this to work at all. If someone could explain how to do this > sort of thing, using ReplacePart or otherwise, I would be most > grateful. > > Scott Morrison > scott@morrison.fl.net.au Here's one method. In[1]:= gt={{3,5},{{},6},{7,{}},{{},{}},{{},56},{{},3}}; In[2]:= b={a1,a2,a3,a4,a5,a6}; In[3]:= sub[p_, b_] := Which[p === {}, b[[j++]], ListQ[p], Map[sub[#, b] &, p], True, p] In[4]:= j = 1; sub[gt, b] Out[4]= {{3, 5}, {a1, 6}, {7, a2}, {a3, a4}, {a5, 56}, {a6, 3}} There are lots of other methods. Dave Withoff Wolfram Research