package batteries
Install
Dune Dependency
Authors
Maintainers
Sources
md5=ea26b5c72e6731e59d856626049cca4d
sha512=55975b62c26f6db77433a3ac31f97af609fc6789bb62ac38b267249c78fd44ff37fe81901f1cf560857b9493a6046dd37b0d1c0234c66bd59e52843aac3ce6cb
doc/batteries.unthreaded/BatDynArray/index.html
Module BatDynArraySource
Dynamic arrays.
A dynamic array is equivalent to an OCaml array that will resize itself when elements are added or removed, except that floats are boxed and that no initialization element is required.
For all the traversal functions (iter, fold, map, etc.), what happens when the array that is being traversed is mutated is not defined.
include BatEnum.Enumerable with type 'a enumerable = 'a t
include BatInterfaces.Mappable with type 'a mappable = 'a t
When an operation on an array fails, Invalid_arg is raised. The integer is the value that made the operation fail, the first string contains the function name that has been called and the second string contains the parameter name that made the operation fail.
Array creation
make count returns an array with some memory already allocated so up to count elements can be stored into it without resizing.
init n f returns an array of n elements filled with values returned by f 0 , f 1, ... f (n-1).
Array manipulation functions
get darr idx gets the element in darr at index idx. If darr has len elements in it, then the valid indexes range from 0 to len-1.
set darr idx v sets the element of darr at index idx to value v. The previous value is overwritten.
upd darr idx f sets the element of darr at index idx to value f (get darr idx)). The previous value is overwritten.
left r len returns the array containing the len first characters of r. If r contains less than len characters, it returns r.
right r len returns the array containing the len last characters of r. If r contains less than len characters, it returns r.
tail r pos returns the array containing all but the pos first characters of r.
insert darr idx v inserts v into darr at index idx. All elements of darr with an index greater than or equal to idx have their index incremented (are moved up one place) to make room for the new element.
add darr v appends v onto the end of darr. v becomes the new last element of darr.
delete darr idx deletes the element of darr at idx. All elements with an index greater than idx have their index decremented (are moved down one place) to fill in the hole.
delete_last darr deletes the last element of darr. This is equivalent of doing delete darr ((length darr) - 1).
delete_range darr idx len deletes len elements starting at index idx. All elements with an index greater than idx+len are moved to fill in the hole.
Alias for delete with parameter order that follows Array.remove_at.
blit src srcidx dst dstidx len copies len elements from src starting with index srcidx to dst starting at dstidx.
compact darr ensures that the space allocated by the array is minimal.
Array copy and conversion
of_enum e returns an array that holds, in order, the elements of e.
range a returns an enumeration of all valid indices of the given array, that is, range a = 0 --^ ((length a) -1 )
of_list lst returns a dynamic array with the elements of lst in it in order.
to_array darr returns the elements of darr in order as an array.
of_array arr returns an array with the elements of arr in it in order.
copy a returns a fresh copy of a, such that no modification of a affects the copy, or vice versa (all new memory is allocated for the copy).
sub a start len returns an array holding the subset of len elements from a starting with the element at index idx.
fill a start len x modifies the array a in place, storing x in elements number start to start + len - 1.
split a converts the array of pairs a into a pair of arrays.
combine a b converts arrays [a0,...aN] [b0,...,bN] into an array of pairs [(a0,b0),...,(aN,bN)].
Array functional support
iter f darr calls the function f on every element of darr. It is equivalent to for i = 0 to length darr - 1 do f (get darr i) done;
iteri f darr calls the function f on every element of darr. It is equivalent to for i = 0 to length darr - 1 do f i (get darr i) done;
map f darr applies the function f to every element of darr and creates a dynamic array from the results - similar to List.map or Array.map.
mapi f darr applies the function f to every element of darr and creates a dynamic array from the results - similar to List.mapi or Array.mapi.
Same as modify, but the function is applied to the index of the element as the first argument, and the element itself as the second argument.
fold_left f x darr computes f ( ... ( f ( f a0 x) a1) ) ... ) aN, where a0,a1..aN are the indexed elements of darr.
fold_right f darr x computes f a0 (f a1 ( ... ( f aN x ) ... ) ) , where a0,a1..aN are the indexed elements of darr.
As fold_left, but with the index of the element as additional argument.
As fold_right, but with the index of the element as additional argument.
reduce f a is fold_left f a0 [a1, ... aN]. This is useful for merging a group of things that have no reasonable default value to return if the group is empty.
keep p darr removes in place all the element x of darr such that p x = false
Note In previous versions, this function used to be called filter. As this caused incompatibilities with comprehension of dynamic arrays, the function name has been changed.
filter p a returns all the elements of the array a that satisfy the predicate p. The order of the elements in the input array is preserved.
Note This function replaces another function called filter, available in previous versions of the library. As the old function was incompatible with comprehension of dynamic arrays, its name was changed to keep.
As filter but with the index passed to the predicate.
filter_map f e returns an array consisting of all elements x such that f y returns Some x , where y is an element of e.
partition p a returns a pair of arrays (a1, a2), where a1 is the array of all the elements of a that satisfy the predicate p, and a2 is the array of all the elements of a that do not satisfy p. The order of the elements in the input array is preserved.
for_all p [a0; a1; ...; an] checks if all elements of the array satisfy the predicate p. That is, it returns (p a0) && (p a1) && ... && (p an).
exists p [a0; a1; ...; an] checks if at least one element of the array satisfies the predicate p. That is, it returns (p a0) || (p a1) || ... || (p an).
find p a returns the first element of array a that satisfies the predicate p.
findi p a returns the index of the first element of array a that satisfies the predicate p.
Same as mem but uses physical equality instead of structural equality to compare array elements.
min_max a returns the (smallest, largest) pair of values from a as judged by Pervasives.compare
kahan_sum l returns a numerically-accurate sum of the floats of l.
You should consider using Kahan summation when you really care about very small differences in the result, while the result or one of the intermediate sums can be very large (which usually results in loss of precision of floating-point addition).
The worst-case rounding error is constant, instead of growing with (the square root of) the length of the input array as with
fsum. On the other hand, processing each element requires four floating-point operations instead of one. See the wikipedia article on Kahan summation for more details.
Operations on two arrays
iter2 f [a0, a1, ..., an] [b0, b1, ..., bn] performs calls f a0 b0, f a1 b1, ..., f an bn in that order.
iter2i f [a0, a1, ..., an] [b0, b1, ..., bn] performs calls f 0 a0 b0, f 1 a1 b1, ..., f n an bn in that order.
Array resizers
The type of a resizer function.
Resizer functions are called whenever elements are added to or removed from the dynamic array to determine what the current number of storage spaces in the array should be. The three named arguments passed to a resizer are the current number of storage spaces in the array, the length of the array before the elements are added or removed, and the length the array will be after the elements are added or removed. If elements are being added, newlength will be larger than oldlength, if elements are being removed, newlength will be smaller than oldlength. If the resizer function returns exactly oldlength, the size of the array is only changed when adding an element while there is not enough space for it.
By default, all dynamic arrays are created with the default_resizer. When a dynamic array is created from another dynamic array (using copy, map , etc. ) the resizer of the copy will be the same as the original dynamic array resizer. To change the resizer, use the set_resizer function.
The default resizer function the library is using - in this version of DynArray, this is the exponential_resizer but should change in next versions.
The exponential resizer- The default resizer except when the resizer is being copied from some other darray.
exponential_resizer works by doubling or halving the number of slots until they "fit". If the number of slots is less than the new length, the number of slots is doubled until it is greater than the new length (or Sys.max_array_size is reached).
If the number of slots is more than four times the new length, the number of slots is halved until it is less than four times the new length.
Allowing darrays to fall below 25% utilization before shrinking them prevents "thrashing". Consider the case where the caller is constantly adding a few elements, and then removing a few elements, causing the length to constantly cross above and below a power of two. Shrinking the array when it falls below 50% would causing the underlying array to be constantly allocated and deallocated. A few elements would be added, causing the array to be reallocated and have a usage of just above 50%. Then a few elements would be remove, and the array would fall below 50% utilization and be reallocated yet again. The bulk of the array, untouched, would be copied and copied again. By setting the threshold at 25% instead, such "thrashing" only occurs with wild swings- adding and removing huge numbers of elements (more than half of the elements in the array).
exponential_resizer is a good performing resizer for most applications. A list allocates 2 words for every element, while an array (with large numbers of elements) allocates only 1 word per element (ignoring unboxed floats). On insert, exponential_resizer keeps the amount of wasted "extra" array elements below 50%, meaning that less than 2 words per element are used. Even on removals where the amount of wasted space is allowed to rise to 75%, that only means that darray is using 4 words per element. This is generally not a significant overhead.
Furthermore, exponential_resizer minimizes the number of copies needed- appending n elements into an empty darray with initial size 0 requires between n and 2n elements of the array be copied- O(n) work, or O(1) work per element (on average). A similar argument can be made that deletes from the end of the array are O(1) as well (obviously deletes from anywhere else are O(n) work- you have to move the n or so elements above the deleted element down).
The stepwise resizer- another example of a resizer function, this time of a parameterized resizer.
The resizer returned by step_resizer step returns the smallest multiple of step larger than newlength if currslots is less then newlength-step or greater than newlength.
For example, to make an darray with a step of 10, a length of len, and a null of null, you would do: make ~resizer:(step_resizer 10) len null
conservative_exponential_resizer is an example resizer function which uses the oldlength parameter. It only shrinks the array on inserts- no deletes shrink the array, only inserts. It does this by comparing the oldlength and newlength parameters. Other than that, it acts like exponential_resizer.
Unsafe operations
*
Boilerplate code
Printing
val print :
?first:string ->
?last:string ->
?sep:string ->
('a BatInnerIO.output -> 'b -> unit) ->
'a BatInnerIO.output ->
'b t ->
unitOperations on DynArray without exceptions.