On Saturday, August 3, 2013 3:37:41 PM UTC-7, Steven D'Aprano wrote:
> On Sat, 03 Aug 2013 13:12:55 -0700, kevin4fong wrote:
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> > Basically, I'm trying to find out how to remove matching items from a
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> > list. But there doesn't seem to be any information on how to go about
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> > doing this specific function.
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> The documentation cannot possibly cover every single one of the infinite
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> number of things somebody might want to do with Python. Programming is
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> about figuring out how to do the things you want from the tools provided
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> by the language.
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> > For example, what I want is:
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> >
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> > let's say there is a list:
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> >
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> > pHands[0] = ['ad', 'ac', 'as', 'ah', '7d', '8s', '9d', 'td', 'js', 'jd']
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> >
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> > So up there, my list, which is named pHands[0] has ten items in it.
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> Ten items? I wouldn't have known that if you didn't say so! *wink*
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>
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> But seriously... you don't need to repeat obvious things like that. We
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> can count as well as you can.
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> But more importantly, it is irrelevant. Is "ten items" important to this
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> problem? No. What if there were nine, or thirty five, or seven? Would the
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> problem of "removing matching items" change? No, the problem remains the
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> same regardless of how many items there are.
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> > I'm trying to make a function where a search is initiated into the list
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> > and any matching items with a first matching number/letter reaching four
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> > are removed
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> In general, rather than removing items from a list, it is faster and
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> safer (less error-prone) to create a new list with the items not removed.
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> But either way, when trying to program, start by thinking about how *you*
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> would do this task by hand:
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> 1) I would start by counting how many items start with each initial
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> letter: in your example I would count those starting with 'a' (4),
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> '7' (1), and so on.
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>
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> 2) Then go through those initial letters, and pick out the ones equal to
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> 4 (or should that be "four or more"?). In this case, only 'a' is 4 or
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> more, but there could be multiple examples, say, 4 'a's and 6 'b's.
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>
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> 3) Then, either delete those items from the original list, *or* make a
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> new list with the remaining items. Making a new list is usually better.
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> Now start turning each step into Python code.
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> Step 1:
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> Iterate over each item, grab the first character of that item, and add
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> one to a counter.
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> counts = {} # Start with an empty dict.
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> for item in pHands[0]:
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> c = item[0] # Grab the first character.
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> if c in counts:
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> counts[c] += 1
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> else:
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> counts[c] = 1
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> This sets the counter to 1 the first time each character is seen,
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> otherwise increments the counter by 1. There's a ready-made tool for
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> doing that:
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> from collections import Counter
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> counts = Counter(item[0] for item in pHands[0])
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>
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> but under the hood, it's essentially doing the same thing as I wrote
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> above.
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> Steps 2 and 3 can be done together:
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> new_list = []
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> for item in pHand[0]:
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> c = item[0]
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> # Look up the character in the counter.
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> if counts[c] < 4:
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> new_list.append(item)
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>
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> pHand[0] = new_list
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> --
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> Steven
Ah, all of the replies were useful but I found yours the most useful because of
all the descriptions and in depth steps so I could actually understand what the
code did. Thank you.
Would you also happen to know how to fit in a simple count for each set of
cards that is removed?
For example, 4a's gone would set the count to 1 but if there was also 4j's, the
count would be at 2.
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