Search for mapping solution

Achim Domma domma at
Sun Jul 6 23:29:38 CEST 2003

"Markus Joschko" <jocsch at> wrote in message
news:bea0fe$2otcq$1 at
> thanks it works. But maybe I can complicate the example a little bit
> (because in real world it's more complicated):
> What if I every list in lines has 20 or more entries and I have only the
> index number to access the name, e.g.
> lines = [['elem1','elem2','fred','elem3',.......;'elem
> 17','333','elem18','0.10'],[...],[...]]

I'm not sure, if I understand you right, but I think you could do it like

nameIndex = 3
costs = {}
for item in lines:
    name = item[nameIndex]
    costs[name] = costs.setdefault(name,0)+float(item[-1])
print costs

This assumes, that the price is always on the last position. Depending on
your requirements there are differnt ways to write it more clearly:

nameIndex = 3
costs = {}
for name,price in [ (x[nameIndex],x[-1]) for x in lines) ]:
    costs[name] = costs.setdefault(name,0)+float(price)

Or something like that:

def priceIter(lines,nameIndex):
    for x in lines: yield x[nameIndex],x[-1]

costs = {}
for name,price in priceIter(lines,3):
    costs[name] = costs.setdefault(name,0)+float(price)

It depends on your situation, what's the best solution for you. Depending on
your control flow it might be convenient do something like this:

def createLinesIter(nameIndex,priceIndex):
    def priceIter(lines,nameIdx=nameIndex,priceIdx=priceIndex):
        for x in lines: yield x[nameIdx],x[priceIdx]

Now you could create special Iterators for your lists an pass them around:

TypA_Iter = createLinesIter(0,-1)
TypB_Iter = creaetLinesIter(3,7)

now you can pass these funtions around with your matching lines list:

def processLines(lines,linesIter):
    costs = {}
    for name,price in linesIter(lines):
        costs[name] = costs.setdefault(name,0)+float(price)
    return costs

And now for your first list:

lines = ....
costs = processLines(lines,TypA_Iter)

The examples are written from head, so there might be some typos. But they
should give you a hint on what's possible in python.


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