Prepend text to beginning of string
var mystr = “Doe”; mystr = “John ” + mystr; Wouldn’t this work for you?
performance
What is the advantage of using forwarding references in range-based for loops?
The only advantage I can see is when the sequence iterator returns a proxy reference and you need to operate on that reference in a non-const way. For example consider: #include <vector> int main() { std::vector<bool> v(10); for (auto& e : v) e = true; } This doesn’t compile because rvalue vector<bool>::reference returned from the … Read more
Times-two faster than bit-shift, for Python 3.x integers?
This seems to be because multiplication of small numbers is optimized in CPython 3.5, in a way that left shifts by small numbers are not. Positive left shifts always create a larger integer object to store the result, as part of the calculation, while for multiplications of the sort you used in your test, a … Read more
Has anyone actually implemented a Fibonacci-Heap efficiently?
The Boost C++ libraries include an implementation of Fibonacci heaps in boost/pending/fibonacci_heap.hpp. This file has apparently been in pending/ for years and by my projections will never be accepted. Also, there have been bugs in that implementation, which were fixed by my acquaintance and all-around cool guy Aaron Windsor. Unfortunately, most of the versions of … Read more
ByteBuffer.allocate() vs. ByteBuffer.allocateDirect()
Ron Hitches in his excellent book Java NIO seems to offer what I thought could be a good answer to your question: Operating systems perform I/O operations on memory areas. These memory areas, as far as the operating system is concerned, are contiguous sequences of bytes. It’s no surprise then that only byte buffers are … Read more
Is String.Format as efficient as StringBuilder
NOTE: This answer was written when .NET 2.0 was the current version. This may no longer apply to later versions. String.Format uses a StringBuilder internally: public static string Format(IFormatProvider provider, string format, params object[] args) { if ((format == null) || (args == null)) { throw new ArgumentNullException((format == null) ? “format” : “args”); } … Read more
Apache Spark: map vs mapPartitions?
Imp. TIP : Whenever you have heavyweight initialization that should be done once for many RDD elements rather than once per RDD element, and if this initialization, such as creation of objects from a third-party library, cannot be serialized (so that Spark can transmit it across the cluster to the worker nodes), use mapPartitions() instead … Read more
Which are more performant, CTE or temporary tables?
It depends. First of all What is a Common Table Expression? A (non recursive) CTE is treated very similarly to other constructs that can also be used as inline table expressions in SQL Server. Derived tables, Views, and inline table valued functions. Note that whilst BOL says that a CTE “can be thought of as … Read more
Why are Python’s arrays slow?
The storage is “unboxed”, but every time you access an element Python has to “box” it (embed it in a regular Python object) in order to do anything with it. For example, your sum(A) iterates over the array, and boxes each integer, one at a time, in a regular Python int object. That costs time. … Read more
String Interpolation vs String.Format
Noticable is relative. However: string interpolation is turned into string.Format() at compile-time so they should end up with the same result. There are subtle differences though: as we can tell from this question, string concatenation in the format specifier results in an additional string.Concat() call.