name_map = {‘oldcol1’: ‘newcol1’, ‘oldcol2’: ‘newcol2’, ‘oldcol3’: ‘newcol3’…} for row in rows: # Each row is a dict of the form: {‘oldcol1’: ‘…’, ‘oldcol2’: ‘…’} row = dict((name_map[name], val) for name, val in row.iteritems()) … Or in Python2.7+ with Dict Comprehensions: for row in rows: row = {name_map[name]: val for name, val in row.items()}
“Random access O(1)” is an extremely exacting requirement which basically imposes an underlying hash table — and I hope you do mean random READS only, because I think it can be mathematically proven than it’s impossible in the general case to have O(1) writes as well as O(N) ordered iteration. I don’t think you will … Read more
Normally if you do a find and maybe an insert, then you want to keep (and retrieve) the old value if it already existed. If you just want to overwrite any old value, map[foo_obj]=”some value” will do that. Here’s how you get the old value, or insert a new one if it didn’t exist, with … Read more
Using breakOut Use breakOut as the CanBuildFrom and let the typer know what you want your result type to be (unfortunately you need to specify String here) scala> import collection.breakOut import collection.breakOut scala> List(1, 2, 3) res0: List[Int] = List(1, 2, 3) scala> res0.map(_.toString)(breakOut) : Vector[String] res2: Vector[String] = Vector(1, 2, 3) Using to[Collection] (starting … Read more
It would be as easy as casting the whole dictionary reference to IReadOnlyDictionary<string, IReadOnlyList<string>> because Dictionary<TKey, TValue> implements IReadOnlyDictionary<TKey, TValue>. BTW, you can’t do that because you want the List<string> values as IReadOnlyList<string>. So you need something like this: var readOnlyDict = (IReadOnlyDictionary<string, IReadOnlyList<string>>)dict .ToDictionary(pair => pair.Key, pair => pair.Value.AsReadOnly()); Immutable dictionaries This is just … Read more
You can also use reduce to insert the separator between every element of the array: render() { let myArray = [1,2,3]; return ( <div> { myArray .map(item => <div>{item}</div>) .reduce((acc, x) => acc === null ? [x] : [acc, ‘ | ‘, x], null) } </div> ); } or using fragments: render() { let myArray … Read more
Actually, in Python 2.7 and 3.2+, this really does work: >>> b = {“foo”, “bar”} >>> b set([‘foo’, ‘bar’]) You can’t use [] access on a set (“key into”), but you can test for inclusion: >>> ‘x’ in b False >>> ‘foo’ in b True Sets are as close to value-less dictionaries as it gets. … Read more
A dictionary comprehension can only ever produce one key-value pair per iteration. The trick then is to produce an extra loop to separate out the pairs: {k: v for e in wp_users for k, v in zip((‘ID’, ‘post_author’), e)} This is equivalent to: result = {} for e in wp_users: for k, v in zip((‘ID’, … Read more
Swift beta 5 has added this functionality, and you’ve nailed the new method in a couple of your attempts. The unwrapping operators ! and ? now pass through the value to either operators or method calls. That is to say, you can add to that array in any of these ways: dict[“key”]! += [4] dict[“key”]!.append(4) … Read more
ConditionalWeakTable Class uses weak keys and automatically removes the key/value entry as soon as no other references to a key exist outside the table.