###### duandushang5148
2017-06-12 08:42 阅读 31

# 在PHP中生成独特的组合

I have a requirement to generate unique combinations from the given data set (n numbers) with each combination contains r values.

Basically looking to implement `C(n,r)=n!(r!(n−r)!)` formula in PHP.

Input data set {A,B,C,D} and need an unique combination of 3 values like below:

``````C(n,r)=C(4,3) = 4!/(3!(4−3)!)
= 4
``````

ABC ACD BCD BDA

(CDA,CAB,BCA etc are duplicates and should be truncated from output).

But my code below

``````<?php
function sampling(\$chars, \$size, \$combinations = array()) {

# if it's the first iteration, the first set
# of combinations is the same as the set of characters
if (empty(\$combinations)) {
\$combinations = \$chars;
}

# we're done if we're at size 1
if (\$size == 1) {
return \$combinations;
}

# initialise array to put new values in
\$new_combinations = array();

# loop through existing combinations and character set to create strings
foreach (\$combinations as \$combination) {
foreach (\$chars as \$char) {
if(\$combination != \$char)
\$new_combinations[] = \$combination . \$char;
}
}

# call same function again for the next iteration
return sampling(\$chars, \$size - 1, \$new_combinations);

}
?>
``````

returns below 64 arrays with duplicates

{ [0]=> string(3) "aaa" [1]=> string(3) "aab" [2]=> string(3) "aac" [3]=> string(3) "aad" [4]=> string(3) "aba" [5]=> string(3) "abb" [6]=> string(3) "abc" [7]=> string(3) "abd" [8]=> string(3) "aca" [9]=> string(3) "acb" [10]=> string(3) "acc" [11]=> string(3) "acd" [12]=> string(3) "ada" [13]=> string(3) "adb" [14]=> string(3) "adc" [15]=> string(3) "add" [16]=> string(3) "baa" [17]=> string(3) "bab" [18]=> string(3) "bac" [19]=> string(3) "bad" [20]=> string(3) "bba" [21]=> string(3) "bbb" [22]=> string(3) "bbc" [23]=> string(3) "bbd" [24]=> string(3) "bca" [25]=> string(3) "bcb" [26]=> string(3) "bcc" [27]=> string(3) "bcd" [28]=> string(3) "bda" [29]=> string(3) "bdb" [30]=> string(3) "bdc" [31]=> string(3) "bdd" [32]=> string(3) "caa" [33]=> string(3) "cab" [34]=> string(3) "cac" [35]=> string(3) "cad" [36]=> string(3) "cba" [37]=> string(3) "cbb" [38]=> string(3) "cbc" [39]=> string(3) "cbd" [40]=> string(3) "cca" [41]=> string(3) "ccb" [42]=> string(3) "ccc" [43]=> string(3) "ccd" [44]=> string(3) "cda" [45]=> string(3) "cdb" [46]=> string(3) "cdc" [47]=> string(3) "cdd" [48]=> string(3) "daa" [49]=> string(3) "dab" [50]=> string(3) "dac" [51]=> string(3) "dad" [52]=> string(3) "dba" [53]=> string(3) "dbb" [54]=> string(3) "dbc" [55]=> string(3) "dbd" [56]=> string(3) "dca" [57]=> string(3) "dcb" [58]=> string(3) "dcc" [59]=> string(3) "dcd" [60]=> string(3) "dda" [61]=> string(3) "ddb" [62]=> string(3) "ddc" [63]=> string(3) "ddd" }

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#### 1条回答默认 最新

• 已采纳
douzhuo8871 2017-06-12 08:59

Say you have a set of 4 items and you want a random subset of 3 of them. You can do the following:

``````\$myset = [ "A","B","C", "D" ];

function randomSubset(\$set, \$size) {
shuffle(\$array);
return array_intersect_key(\$set, array_filter(\$array));
}

print_r(randomSubset(\$myset,3));
``````

Now if you need all subsets of size N you can do some recursive magic:

``````function allSubsets(\$set, \$size) {
\$subsets = [];
if (\$size == 1) {
return array_map(function (\$v) { return [\$v]; },\$set);
}
foreach (allSubsets(\$set,\$size-1) as \$subset) {
foreach (\$set as \$element) {
if (!in_array(\$element,\$subset)) {
\$newSet = array_merge(\$subset,[\$element]);
sort(\$newSet);
if (!in_array(\$newSet,\$subsets)) {
\$subsets[] = array_merge(\$subset,[\$element]);
}
}
}
}
return \$subsets;

}

\$myset = [ "A","B","C", "D", "E" ];
print_r(allSubsets(\$myset,3));
``````
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