Add value in list of list c#
Pairs and Lists in The Racket Guide introduces pairs and lists.
A pair combines exactly two values. The first value is accessed with the car procedure, and the second value is accessed with the cdr procedure. Pairs are not mutable [but see Mutable Pairs and Lists].
A list is recursively defined: it is either the constant null, or it is a pair whose second value is a list.
A list can be used as a single-valued sequence [see Sequences]. The elements of the list serve as elements of the sequence. See also in-list.
Cyclic data structures can be created using only immutable pairs via read or make-reader-graph. If starting with a pair and using some number of cdrs returns to the starting pair, then the pair is not a list.
See Reading Pairs and Lists for information on reading pairs and lists and Printing Pairs and Lists for information on printing pairs and lists.
4.10.1Pair Constructors and Selectors
Returns #t if v is a pair, #f otherwise.
Returns #t if v is the empty list, #f otherwise.
Returns a newly allocated pair whose first element is a and second element is d.
Returns the first element of the pair p.
Returns the second element of the pair p.
Returns #t if v is a list: either the empty list, or a pair whose second element is a list. This procedure effectively takes constant time due to internal caching [so that any necessary traversals of pairs can in principle count as an extra cost of allocating the pairs].
Returns a newly allocated list containing the vs as its elements.
Like list, but the last argument is used as the tail of the result, instead of the final element. The result is a list only if the last argument is a list.
Creates a list of n elements by applying proc to the integers from 0 to [sub1 n] in order. If lst is the resulting list, then [list-ref lst i] is the value produced by [proc i].
4.10.2List Operations
Returns the number of elements in lst. This function takes time proportional to that length.
Returns the element of lst at position pos, where the lists first element is position 0. If the list has pos or fewer elements, then the exn:fail:contract exception is raised.
The lst argument need not actually be a list; lst must merely start with a chain of at least [add1 pos] pairs.
This function takes time proportional to pos.
Returns the list after the first pos elements of lst. If the list has fewer than pos elements, then the exn:fail:contract exception is raised.
The lst argument need not actually be a list; lst must merely start with a chain of at least pos pairs.
This function takes time proportional to pos.
When given all list arguments, the result is a list that contains all of the elements of the given lists in order. The last argument is used directly in the tail of the result.
The last argument need not be a list, in which case the result is an improper list.
This function takes time proportional to the length of all arguments [added together] except the last argument.
Returns a list that has the same elements as lst, but in reverse order.
This function takes time proportional to the length of lst.
4.10.3List Iteration
Applies proc to the elements of the lsts from the first elements to the last. The proc argument must accept the same number of arguments as the number of supplied lsts, and all lsts must have the same number of elements. The result is a list containing each result of proc in order.
'[2 3 4 5] |
| > [map[lambda[number1number2] | | [+number1number2]] | | '[1234] | | '[10100100010000]] |
|
'[11 102 1003 10004] |
Similar to map in the sense that proc is applied to each element of lst, but
The andmap function is actually closer to foldl than map, since andmap doesnt produce a list. Still, [andmap f [list x y z]] is equivalent to [and [f x] [f y] [f z]] in the same way that [map f [list x y z]] is equivalent to [list [f x] [f y] [f z]].
the result is #f if any application of proc produces #f, in which case proc is not applied to later elements of the lsts; and
the result is that of proc applied to the last elements of the lsts; more specifically, the application of proc to the last elements in the lsts is in tail position with respect to the andmap call.
If the lsts are empty, then #t is returned.
Similar to map in the sense that proc is applied to each element of lst, but
To continue the andmap note above, [ormap f [list x y z]] is equivalent to [or [f x] [f y] [f z]].
the result is #f if every application of proc produces #f; and
the result is that of the first application of proc producing a value other than #f, in which case proc is not applied to later elements of the lsts; the application of proc to the last elements of the lsts is in tail position with respect to the ormap call.
If the lsts are empty, then #f is returned.
Similar to map, but proc is called only for its effect, and its result [which can be any number of values] is ignored.
Like map, foldl applies a procedure to the elements of one or more lists. Whereas map combines the return values into a list, foldl combines the return values in an arbitrary way that is determined by proc.
If foldl is called with n lists, then proc must take n+1 arguments. The extra argument is the combined return values so far. The proc is initially invoked with the first item of each list, and the final argument is init. In subsequent invocations of proc, the last argument is the return value from the previous invocation of proc. The input lsts are traversed from left to right, and the result of the whole foldl application is the result of the last application of proc. If the lsts are empty, the result is init.
Unlike foldr, foldl processes the lsts in constant space [plus the space for each call to proc].
Like foldl, but the lists are traversed from right to left. Unlike foldl, foldr processes the lsts in space proportional to the length of lsts [plus the space for each call to proc].
4.10.4List Filtering
Returns a list with the elements of lst for which pred produces a true value. The pred procedure is applied to each element from first to last.
Returns a list that is like lst, omitting the first element of lst that is equal to v using the comparison procedure proc [which must accept two arguments], with v as the first argument and an element in lst as the second argument. If no element in lst is equal to v [according to proc], lst is returned unchanged.
Changed in version 8.2.0.2 of package base: Guaranteed that the output is eq? to lst if no removal occurs.
Like remove, but removes from lst every instance of every element of v-lst.
Changed in version 8.2.0.2 of package base: Guaranteed that the output is eq? to lst if no removal occurs.
Returns a list sorted according to the less-than? procedure, which takes two elements of lst and returns a true value if the first is less [i.e., should be sorted earlier] than the second.
The sort is stable; if two elements of lst are equal [i.e., less-than? does not return a true value when given the pair in either order], then the elements preserve their relative order from lst in the output list. To preserve this guarantee, use sort with a strict comparison functions [e.g., < or string; not [sort'["aardvark""dingo""cow""bear"]string]
'["aardvark" "bear" "cow" "dingo"] |
'[["aardvark"] ["bear"] ["cow"] ["dingo"]]
|
4.10.5List SearchingLocates the first element of lst that is equal? to v. If such an element exists, the tail of lst starting with that element is returned. Otherwise, the result is #f.
The lst argument need not actually be a list; lst must merely start with a chain of pairs until a matching element is found. If no matching element is found, then lst must be a list [and not a cyclic list]. The result can be a non-list in the case that an element is found and the returned tail of lst is a non-list.
Like member, but finds an element using the predicate proc; an element is found when proc applied to the element returns a true value.
Like memf, but returns the element or #f instead of a tail of lst or #f.
Locates the first element of lst whose car is equal to v according to is-equal?. If such an element exists, the pair [i.e., an element of lst] is returned. Otherwise, the result is #f.
The lst argument need not actually be a list of pairs; lst must merely start with a chain of pairs contains pairs until a matching element is found. If no matching element is found, then lst must be a list of pairs [and not a cyclic list].
Like assoc, but finds an element using eq?.
Like assoc, but finds an element using the predicate proc; an element is found when proc applied to the car of an lst element returns a true value.
4.10.6Pair Accessor Shorthands| > [cdar'[[7654321]89]] |
'[6 5 4 3 2 1] |
| > [caaar'[[[654321]7]89]] |
6 |
| > [cdaar'[[[654321]7]89]] |
'[5 4 3 2 1] |
| > [cdadr'[9[7654321]8]] |
'[6 5 4 3 2 1] |
| > [cddar'[[7654321]89]] |
'[5 4 3 2 1] |
| > [cdaaar'[[[[54321]6]7]89]] |
'[4 3 2 1] |
| > [cdaadr'[9[[654321]7]8]] |
'[5 4 3 2 1] |
| > [cdadar'[[7[54321]6]89]] |
'[4 3 2 1] |
| > [cdaddr'[98[654321]7]] |
'[5 4 3 2 1] |
| > [cddaar'[[[654321]7]89]] |
'[4 3 2 1] |
| > [cddadr'[9[7654321]8]] |
'[5 4 3 2 1] |
| > [cdddar'[[7654321]89]] |
'[4 3 2 1] |
The same as [car lst], but only for lists [that are not empty].
The same as [cdr lst], but only for lists [that are not empty].
| > [rest'[12345678910]] |
'[2 3 4 5 6 7 8 9 10] |
Returns the second element of the list.
Returns the third element of the list.
Returns the fourth element of the list.
Returns the fifth element of the list.
Returns the sixth element of the list.
Returns the seventh element of the list.
Returns the eighth element of the list.
Returns the ninth element of the list.
Returns the tenth element of the list.
Returns the last element of the list.
This function takes time proportional to the length of lst.
Returns the last pair of a [possibly improper] list.
This function takes time proportional to the length of p.
Returns a newly constructed list of length k, holding v in all positions.
| > [make-list7'foo] |
'[foo foo foo foo foo foo foo] |
Returns a list that is the same as lst except at the specified index. The element at the specified index is [updater [list-ref lst pos]].
This function takes time proportional to pos.
Added in version 6.3 of package base.
Returns a list that is the same as lst except at the specified index. The element at the specified index is value.
This function takes time proportional to pos.
| > [list-set'[zeroonetwo]2"two"] |
'[zero one "two"] |
Added in version 6.3 of package base.
Like member, but returns the index of the first element found instead of the tail of the list.
Added in version 6.7.0.3 of package base.
Like index-of but with the predicate-searching behavior of memf.
Added in version 6.7.0.3 of package base.
Like index-of, but returns the a list of all the indexes where the element occurs in the list instead of just the first one.
Added in version 6.7.0.3 of package base.
Added in version 6.7.0.3 of package base.
Returns a fresh list whose elements are the first pos elements of lst. If lst has fewer than pos elements, the exn:fail:contract exception is raised.
The lst argument need not actually be a list; lst must merely start with a chain of at least pos pairs.
This function takes time proportional to pos.
| > [take'[12345]2] |
'[1 2]
|
| > [take'non-list0] |
'[] |
Returns the same result as
[values[takelstpos][droplstpos]]
except that it can be faster, but it will still take time proportional to pos.
Returns a fresh list whose elements are taken successively from lst as long as they satisfy pred. The returned list includes up to, but not including, the first element in lst for which pred returns #f.
The lst argument need not actually be a list; the chain of pairs in lst will be traversed until a non-pair is encountered.
Drops elements from the front of lst as long as they satisfy pred.
Returns the same result as
[values[takeflstpred][dropflstpred]]
except that it can be faster.
Returns the lists pos-length tail. If lst has fewer than pos elements, then the exn:fail:contract exception is raised.
The lst argument need not actually be a list; lst must merely end with a chain of at least pos pairs.
This function takes time proportional to the length of lst.
Returns a fresh list whose elements are the prefix of lst, dropping its pos-length tail. If lst has fewer than pos elements, then the exn:fail:contract exception is raised.
The lst argument need not actually be a list; lst must merely end with a chain of at least pos pairs.
This function takes time proportional to the length of lst.
Returns the same result as
[values[drop-rightlstpos][take-rightlstpos]]
except that it can be faster, but it will still take time proportional to the length of lst.
Added in version 6.3 of package base.
Returns the longest common prefix of l and r.
Added in version 6.3 of package base.
Returns the tails of l and r with the common prefix removed.
Added in version 6.3 of package base.
Returns the longest common prefix together with the tails of l and r with the common prefix removed.
Added in version 6.3 of package base.
Returns a list with the same elements as lst, but with v between each pair of elements in lst; the last pair of elements will have before-last between them, instead of v [but before-last defaults to v].
If splice? is true, then v and before-last should be lists, and the list elements are spliced into the result. In addition, when splice? is true, before-first and after-last are inserted before the first element and after the last element respectively.
| > [add-between'[xyz]'and] |
'[x and y and z] |
| > [add-between'[x]'and] |
'[x] |
| > [add-between'["a""b""c""d"]","#:before-last"and"] |
'["a" "," "b" "," "c" "and" "d"] |
| > [add-between'[xyz]'[-]#:before-last'[--] | | #:before-first'[begin]#:after-last'[endLF] | | #:splice?#t] |
|
'[begin x - y - - z end LF] |
| > [append*'[a]'[b]'[[c][d]]] |
'[a b c d] |
'["Alpha" ", " "Beta" ", " "Gamma"] |
Flattens an arbitrary S-expression structure of pairs into a list. More precisely, v is treated as a binary tree where pairs are interior nodes, and the resulting list contains all of the non-null leaves of the tree in the same order as an inorder traversal.
Returns the first duplicate item in lst. More precisely, it returns the first x such that there was a previous y where [same? [extract-key x] [extract-key y]].
If no duplicate is found, then failure-result determines the result:
If failure-result is a procedure, it is called [through a tail call] with no arguments to produce the result.
Otherwise, failure-result is returned as the result.
The same? argument should be an equivalence predicate such as equal? or eqv? or a dictionary. The procedures equal?, eqv?, and eq? automatically use a dictionary for speed.
Added in version 6.3 of package base.
Changed in version 6.11.0.2: Added the #:default optional argument.
Returns a list that has all items in lst, but without duplicate items, where same? determines whether two elements of the list are equivalent. The resulting list is in the same order as lst, and for any item that occurs multiple times, the first one is kept.
The #:key argument extract-key is used to extract a key value from each list element, so two items are considered equal if [same? [extract-key x] [extract-key y]] is true.
Like [map proc lst ...], except that, if proc returns #false, that element is omitted from the resulting list. In other words, filter-map is equivalent to [filter [lambda [x] x] [map proc lst ...]], but more efficient, because filter-map avoids building the intermediate list.
Similar to filter, except that two values are returned: the items for which pred returns a true value, and the items for which pred returns #f.
The result is the same as
[values[filterpredlst][filter[negatepred]lst]]
but pred is applied to each item in lst only once.
The resulting list holds numbers starting at start and whose successive elements are computed by adding step to their predecessor until end [excluded] is reached. If no starting point is provided, 0 is used. If no step argument is provided, 1 is used.
Like in-range, a range application can provide better performance when it appears directly in a for clause.
| > [range10] |
'[0 1 2 3 4 5 6 7 8 9] |
| > [range1020] |
'[10 11 12 13 14 15 16 17 18 19] |
| > [range20402] |
'[20 22 24 26 28 30 32 34 36 38] |
| > [range2010-1] |
'[20 19 18 17 16 15 14 13 12 11] |
| > [range10151.5] |
'[10 11.5 13.0 14.5] |
Changed in version 6.7.0.4 of package base: Adjusted to cooperate with for in the same way that in-range does.
The resulting list holds numbers starting at start and whose successive elements are computed by adding step to their predecessor until end [included] is reached. If no step argument is provided, 1 is used.
Like in-inclusive-range, an inclusive-range application can provide better performance when it appears directly in a for clause.
Added in version 8.0.0.13 of package base.
Like filter, but the meaning of the pred predicate is reversed: the result is a list of all items for which pred returns #f.
Returns a list with all elements from lst, randomly shuffled.
Return a list of all combinations of elements in the input list [aka the powerset of lst]. If size is given, limit results to combinations of size elements.
Returns a sequence of all combinations of elements in the input list, or all combinations of length size if size is given. Builds combinations one-by-one instead of all at once.
Returns a list of all permutations of the input list. Note that this function works without inspecting the elements, and therefore it ignores repeated elements [which will result in repeated permutations]. Raises an error if the input list contains more than 256 elements.
Returns a sequence of all permutations of the input list. It is equivalent to [in-list [permutations l]] but much faster since it builds the permutations one-by-one on each iteration. Raises an error if the input list contains more than 256 elements.
Returns the first element in the list lst that minimizes the result of proc. Signals an error on an empty list. See also min.
| > [argmincar'[[3pears][1banana][2apples]]] |
'[1 banana] |
| > [argmincar'[[1banana][1orange]]] |
'[1 banana] |
Returns the first element in the list lst that maximizes the result of proc. Signals an error on an empty list. See also max.
| > [argmaxcar'[[3pears][1banana][2apples]]] |
'[3 pears] |
| > [argmaxcar'[[3pears][3oranges]]] |
'[3 pears] |
Groups the given list into equivalence classes, with equivalence being determined by same?. Within each equivalence class, group-by preserves the ordering of the original list. Equivalence classes themselves are in order of first appearance in the input.
Added in version 6.3 of package base.
Computes the n-ary cartesian product of the given lists.
| > [cartesian-product'[123]'[abc]] |
'[[1 a] [1 b] [1 c] [2 a] [2 b] [2 c] [3 a] [3 b] [3 c]] |
| > [cartesian-product'[456]'[def]'[#t#f]] |
'[[4 d #t] | [4 d #f] | [4 e #t] | [4 e #f] | [4 f #t] | [4 f #f] | [5 d #t] | [5 d #f] | [5 e #t] | [5 e #f] | [5 f #t] | [5 f #f] | [6 d #t] | [6 d #f] | [6 e #t] | [6 e #f] | [6 f #t] | [6 f #f]] |
|
Added in version 6.3 of package base.
Returns a list that is like lst, omitting the first element of lst for which pred produces a true value.
Added in version 6.3 of package base.
Like remf, but removes all the elements for which pred produces a true value.
Added in version 6.3 of package base.
Returns a value like v, with placeholders created by make-placeholder replaced with the values that they contain, and with placeholders created by make-hash-placeholder with an immutable hash table. No part of v is mutated; instead, parts of v are copied as necessary to construct the resulting graph, where at most one copy is created for any given value.
Since the copied values can be immutable, and since the copy is also immutable, make-reader-graph can create cycles involving only immutable pairs, vectors, boxes, and hash tables.
Only the following kinds of values are copied and traversed to detect placeholders:
Due to these restrictions, make-reader-graph creates exactly the same sort of cyclic values as read.
Changes the value of ph to v.
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