It’s a feature. .NET 4.0 only supports safe covariance. The cast you mentioned is potentially dangerous as you could add a non-string element to the dictionary if that was possible: IDictionary<string, object> myDict = new Dictionary<string, string>(); myDict[“hello”] = 5; // not an string On the other hand, IEnumerable<T> is a read-only interface. The T … Read more
will my program crash because the int in my map is unitialized? No; if the element with key word doesn’t exist, the element will be created and value initialized. A value-initialized int has a value of 0.
In Python, every iterable can be unpacked1: >>> x,y,z = [1, 2, 3] # A list >>> x,y,z (1, 2, 3) >>> x,y,z = 1, 2, 3 # A tuple >>> x,y,z (1, 2, 3) >>> x,y,z = {1:’a’, 2:’b’, 3:’c’} # A dictionary >>> x,y,z (1, 2, 3) >>> x,y,z = (a for a … Read more
If using Visual Studio 2010 or later you should use the FROM keyword like this: Dim days = New Dictionary(Of Integer, String) From {{0, “string”}, {1, “string2”}} See: http://msdn.microsoft.com/en-us/library/dd293617(VS.100).aspx If you need to use a prior version of Visual Studio and you need to do this frequently you could just inherit from the Dictionary class … Read more
Just switch the order: z = dict(d2.items() + d1.items()) By the way, you may also be interested in the potentially faster update method. In Python 3, you have to cast the view objects to lists first: z = dict(list(d2.items()) + list(d1.items())) If you want to special-case empty strings, you can do the following: def mergeDictsOverwriteEmpty(d1, … Read more
The whole point of using Maps is direct access. If you know for sure that the value in a map will never be Groovy-false, then you can do this: def mymap = [name:”Gromit”, likes:”cheese”, id:1234] def key = “likes” if(mymap[key]) { println mymap[key] } However, if the value could potentially be Groovy-false, you should use: … Read more
You can use the function for plotting histograms like this: a = np.random.random_integers(0,10,20) #example list of values plt.hist(a) plt.show() Or you can use myDictionary just like this: plt.bar(myDictionary.keys(), myDictionary.values(), width, color=”g”)
If you’re using .net 3.5, Enumerable has an extension method ElementAt which would allow you to do: return dict.ElementAt(rand.Next(0, dict.Count)).Value;
Assuming you’re using .NET 3.5: dic.Keys.First(); Note that there’s no guaranteed order in which key/value pairs will be iterated over in a dictionary. You may well find that in lots of cases you get out the first key that you put into the dictionaries – but you absolutely must not rely on that. As Skirwan … Read more
You can also rely on django code already written ;). from django.forms.models import model_to_dict model_to_dict(instance, fields=[], exclude=[])