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Of the two given pairs of comparisons, Which one (of each pair) is more expensive to System Resources in Erlang:
Qn1: lists:append(L1,L2) versus erlang:'++'(L1,L2)
Qn2 Writing to the head of a list with say: [NewHead|List] versus writing to the end of the list with: List ++ [NewValue]
I have asked this because there is an intensive part of my program which will be reading and writing into lists. I need to decide wether i will be writing to the lists' heads or writing to their ends, or vice versa.
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If we want to add an element at the end of a list, we should use append . It is faster and direct. If we want to add an element somewhere within a list, we should use insert . It is the only option for this.
For large lists with one million elements, the runtime of the extend() method is 60% faster than the runtime of the append() method.
Python's append() function inserts a single element into an existing list. The element will be added to the end of the old list rather than being returned to a new list. Adds its argument as a single element to the end of a list.
1: They are the same function. 'append' is an alias for '++' (or vice versa). See also Erlang ++ operator. Syntactic sugar, or separate operation?
2: Don't build a list incrementally by appending. Appending once is OK, but appending in a loop will give you quadratic behaviour. I.e., AddedStuff ++ Accumulator is OK (even in a loop), because you're growing "to the left", but Accumulator ++ AddedStuff in a loop (growing to the right) is really bad. It's much better to grow to the left and then reverse or sort afterwards if the order is important.
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