Generate All Combinations Of Key Value Pairs Java
- Generate All Combinations Of Key Value Pairs Javascript
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- Generate All Combinations Of Key Value Pairs Java 1
How to generate unique combinations in Excel? Supposing you have three lists, and now you want to generate unique combinations from these three lists as below screenshots shown, and how can you quickly solve this troublesome problem in Excel? Then in the List All Combinations dialog, select Value from Type drop down list. Key-Value Pair: A key-value pair (KVP) is an abstract data type that includes a group of key identifiers and a set of associated values. Key-value pairs are frequently used in lookup tables, hash tables and configuration files.
I have a list with 15 numbers in, and I need to write some code that produces all 32,768 combinations of those numbers.
I’ve found some code (by Googling) that apparently does what I’m looking for, but I found the code fairly opaque and am wary of using it. Plus I have a feeling there must be a more elegant solution.
The only thing that occurs to me would be to just loop through the decimal integers 1–32768 and convert those to binary, and use the binary representation as a filter to pick out the appropriate numbers.
Does anyone know of a better way? Using map()
, maybe?
Have a look at itertools.combinations:
Return r length subsequences of elements from
the input iterable.
Combinations are emitted in lexicographic sort order. So, if the
input iterable is sorted, the
combination tuples will be produced in
sorted order.
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This answer missed one aspect: the OP asked for ALL combinations… not just combinations of length “r”.
So you’d either have to loop through all lengths “L”:
Or — if you want to get snazzy (or bend the brain of whoever reads your code after you) — you can generate the chain of “combinations()” generators, and iterate through that:
Here’s a lazy one-liner, also using itertools:
Main idea behind this answer: there are 2^N combinations — same as the number of binary strings of length N. For each binary string, you pick all elements corresponding to a “1”.
Things to consider:
- This requires that you can call
len(..)
onitems
(workaround: ifitems
is something like an iterable like a generator, turn it into a list first withitems=list(_itemsArg)
) - This requires that the order of iteration on
items
is not random (workaround: don’t be insane) - This requires that the items are unique, or else
{2,2,1}
and{2,1,1}
will both collapse to{2,1}
(workaround: usecollections.Counter
as a drop-in replacement forset
; it’s basically a multiset… though you may need to later usetuple(sorted(Counter(..).elements()))
if you need it to be hashable)
Demo
I agree with Dan H that Ben indeed asked for all combinations. itertools.combinations()
does not give all combinations.
Another issue is, if the input iterable is big, it is perhaps better to return a generator instead of everything in a list:
This one-liner gives you all the combinations (between 0
and n
items if the original list/set contains n
distinct elements) and uses the native method itertools.combinations
:
The output will be:
Try it online:
In comments under the highly upvoted answer by @Dan H, mention is made of the powerset()
recipe in the itertools
documentation—including one by Dan himself. However, so far no one has posted it as an answer. Since it’s probably one of the better if not the best approach to the problem—and given a little encouragement from another commenter, it’s shown below. The function produces all unique combinations of the list elements of every length possible.
Note: If the, subtly different, goal is to obtain only combinations of unique elements, change the line s = list(iterable)
to s = list(set(iterable))
to eliminate any duplicate elements. Regardless, the fact that the iterable
is ultimately turned into a list
means it will work with generators (unlike several of the other answers).
Output:
You can generating all combinations of a list in python using this simple code
Result would be :
Here is yet another solution (one-liner), involving using the itertools.combinations
function, but here we use a double list comprehension (as opposed to a for loop or sum):
Demo:
Below is a “standard recursive answer”, similar to the other similar answer https://stackoverflow.com/a/23743696/711085 . (We don’t realistically have to worry about running out of stack space since there’s no way we could process all N! permutations.)
It visits every element in turn, and either takes it or leaves it (we can directly see the 2^N cardinality from this algorithm).
Demo:
I thought I would add this function for those seeking an answer without importing itertools or any other extra libraries.
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Simple Yield Generator Usage:
Output from Usage example above:
[] , [1] , [2] , [1, 2] , [3] , [1, 3] , [2, 3] , [1, 2, 3] , [4] ,
[1, 4] , [2, 4] , [1, 2, 4] , [3, 4] , [1, 3, 4] , [2, 3, 4] , [1, 2,
3, 4] ,
This code employs a simple algorithm with nested lists…
I know it’s far more practical to use itertools to get the all the combinations, but you can achieve this partly with only list comprehension if you so happen to desire, granted you want to code a lot
For combinations of two pairs:
And, for combinations of three pairs, it’s as easy as this:
The result is identical to using itertools.combinations:
In order to be able to create a digital signature, you need a private key. (Its corresponding public key will be needed in order to verify the authenticity of the signature.)
In some cases the key pair (private key and corresponding public key) are already available in files. In that case the program can import and use the private key for signing, as shown in Weaknesses and Alternatives.
In other cases the program needs to generate the key pair. A key pair is generated by using the KeyPairGenerator
class.
In this example you will generate a public/private key pair for the Digital Signature Algorithm (DSA). You will generate keys with a 1024-bit length.
Generating a key pair requires several steps:
Create a Key Pair Generator
The first step is to get a key-pair generator object for generating keys for the DSA signature algorithm.
As with all engine classes, the way to get a KeyPairGenerator
object for a particular type of algorithm is to call the getInstance
static factory method on the KeyPairGenerator
class. This method has two forms, both of which hava a String algorithm
first argument; one form also has a String provider
second argument.
A caller may thus optionally specify the name of a provider, which will guarantee that the implementation of the algorithm requested is from the named provider. The sample code of this lesson always specifies the default SUN provider built into the JDK.
Put the following statement after the
line in the file created in the previous step, Prepare Initial Program Structure:
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Initialize the Key Pair Generator
The next step is to initialize the key pair generator. All key pair generators share the concepts of a keysize and a source of randomness. The KeyPairGenerator
class has an initialize
method that takes these two types of arguments.
The keysize for a DSA key generator is the key length (in bits), which you will set to 1024.
The source of randomness must be an instance of the SecureRandom
class that provides a cryptographically strong random number generator (RNG). For more information about SecureRandom
, see the SecureRandom API Specification and the Java Cryptography Architecture Reference Guide .
The following example requests an instance of SecureRandom
that uses the SHA1PRNG algorithm, as provided by the built-in SUN provider. The example then passes this SecureRandom
instance to the key-pair generator initialization method.
Generate All Combinations Of Key Value Pairs Javascript
Some situations require strong random values, such as when creating high-value and long-lived secrets like RSA public and private keys. To help guide applications in selecting a suitable strong SecureRandom
implementation, starting from JDK 8 Java distributions include a list of known strong SecureRandom
implementations in the securerandom.strongAlgorithms
property of the java.security.Security
class. When you are creating such data, you should consider using SecureRandom.getInstanceStrong()
, as it obtains an instance of the known strong algorithms.
Generate All Combinations Of Key Value Pairs Java Download
Generate the Pair of Keys
Generate All Combinations Of Key Value Pairs Java 1
The final step is to generate the key pair and to store the keys in PrivateKey
and PublicKey
objects.