How do I encode a JavaScript object as JSON?
I think you can use JSON.stringify: // after your each loop JSON.stringify(values);
hashtable
Hash table – why is it faster than arrays?
In cases where I have a key for each element and I don’t know the index of the element into an array, hashtables perform better than arrays (O(1) vs O(n)). The hash table search performs O(1) in the average case. In the worst case, the hash table search performs O(n): when you have collisions and … Read more
Why does my Intel Skylake / Kaby Lake CPU incur a mysterious factor 3 slowdown in a simple hash table implementation?
Summary The TLDR is that loads which miss all levels of the TLB (and so require a page walk) and which are separated by address unknown stores can’t execute in parallel, i.e., the loads are serialized and the memory level parallelism (MLP) factor is capped at 1. Effectively, the stores fence the loads, much as … Read more
Why is accessing an element of a dictionary by key O(1) even though the hash function may not be O(1)?
O(1) doesn’t mean instant. O(1) means constant without regard to the size of the data. The hash function takes a certain amount of time, but that amount of time doesn’t scale with the size of the collection.
Hashtable with MultiDimensional Key in C#
I think a better approach is to encapsulate the many fields of your multi-dimensional key into a class / struct. For example struct Key { public readonly int Dimension1; public readonly bool Dimension2; public Key(int p1, bool p2) { Dimension1 = p1; Dimension2 = p2; } // Equals and GetHashCode ommitted } Now you can … Read more
Why are there no hashtables in the C standard library?
C seems unusual by today’s standards because there are no useful data structures defined. None. Not even strings — and if you think a C string is a data structure, well, we’ll have to disagree on what a “data structure” is. If you like C, then think of it as a “blank slate”… your entire … Read more
Does “put” overwrite existing values?
Yes. If a mapping to the specified key already exists, the old value will be replaced (and returned). See Hashtable.put(). For multi-threaded environment, I’d recommend ConcurrentHashMap or another ConcurrentMap implementation. Though Hashtable is synchronized, there are more sophisticated implementations available now for concurrent mapping, such as Guava’s MapMaker and CacheBuilder. Also keep in mind the … Read more
Hash tables VS associative arrays
In PHP, associative arrays are implemented as hashtables, with a bit of extra functionality. However technically speaking, an associative array is not identical to a hashtable – it’s simply implemented in part with a hashtable behind the scenes. Because most of its implementation is a hashtable, it can do everything a hashtable can – but … Read more
PSCustomObject to Hashtable
Shouldn’t be too hard. Something like this should do the trick: # Create a PSCustomObject (ironically using a hashtable) $ht1 = @{ A = ‘a’; B = ‘b’; DateTime = Get-Date } $theObject = new-object psobject -Property $ht1 # Convert the PSCustomObject back to a hashtable $ht2 = @{} $theObject.psobject.properties | Foreach { $ht2[$_.Name] = … Read more
Hash tables in MATLAB
Consider using MATLAB’s map class: containers.Map. Here is a brief overview: Creation: >> keys = {‘Jan’, ‘Feb’, ‘Mar’, ‘Apr’, ‘May’, ‘Jun’, … ‘Jul’, ‘Aug’, ‘Sep’, ‘Oct’, ‘Nov’, ‘Dec’, ‘Annual’}; >> values = {327.2, 368.2, 197.6, 178.4, 100.0, 69.9, … 32.3, 37.3, 19.0, 37.0, 73.2, 110.9, 1551.0}; >> rainfallMap = containers.Map(keys, values) rainfallMap = containers.Map handle … Read more