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# Building all combinations of a vector - looking for a nicer way

By : noahcartersc
Date : November 21 2020, 07:01 PM
hop of those help? I have a simple case which I could solve in an ugly way, but I am sure a much cleverer (and faster) way must exist. , Loud debugging? I just found this way
code :
``````as.data.frame(t(combn(d,m=2)))

V1 V2
1   1  2
2   1  3
3   1  4
4   1  5
5   1  6
6   2  3
7   2  4
8   2  5
9   2  6
10  3  4
11  3  5
12  3  6
13  4  5
14  4  6
15  5  6
``````

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## Building a Matrix of Combinations

By : Trofim
Date : March 29 2020, 07:55 AM
wish help you to fix your issue OK, you want a sequence containing all 720 possible sequences. This is a bit trickier but it can be done.
The basic idea is the same as in my previous answer. In that answer we:
code :
``````Permutations<string> permutations = new Permutations<string>(foods);
``````
``````IEnumerable<List<Pair>> query =
from permutation in permutations
select colors.Zip(permutation, (color, food)=>new Pair(color, food)).ToList();
``````
``````List<List<Pair>> results = query.ToList();
``````

## Determining all sub-vector combinations of a binary vector for a certain hamming weight

By : Walter Sanchez
Date : March 29 2020, 07:55 AM
To fix this issue The easiest way to approach this problem is to fetch all the non zero element indexes and thereby find a combinations of size y, of all these indexes.
For example:
code :
``````for i in index:
binary_seq[i] = '0'
``````
``````def foo(bin_seq, y):
from itertools import combinations
bin_seq = list(bin_seq)
y = bin_seq.count('1') - y
indexes = [i for i in range(len(bin_seq)) if bin_seq[i] == '1']
for index in combinations(indexes,  y):
vec = bin_seq[:]
for i in index:
vec[i] = '0'
yield ''.join(vec)
``````
``````>>> list(foo('0110110', 3))
['0010110', '0100110', '0110010', '0110100']
>>> list(foo('0110110', 2))
['0000110', '0010010', '0010100', '0100010', '0100100', '0110000']
``````

## Is there a nicer way of building an OracleCommand?

By : user2728683
Date : March 29 2020, 07:55 AM
I hope this helps . I haven't tried this, but you should be able to do some linq fanciness with that loop and if condition:
code :
``````string selectStatement = "SELECT " + string.Join(", ", allC
.Where(c => c.IsChecked.GetValueOrDefault())
.Select(c => c.Content));
``````

## R: Building Conditional Combinations

By : user3378194
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further You can do this by using a merge, and reduce to loop over it.
At each level you will need to specify only the values you want to join on:
code :
``````level.1 <- data.frame(country = c("Netherlands", "New Zealand", "Europe"))
level.2 <- data.frame(country = c("Europe"), city = c('paris','london' ))
level.3 <- data.frame(country = c('Europe'), location = c('city', 'roads'))
level.4 <- data.frame(country = c('Europe'), regulation = c("A-Regulated", "G-Regulated", "C-Regulated"))
``````
``````Reduce(function(x, y) merge(x, y, all=TRUE), list(level.1, level.2, level.3, level.4))

country   city location  regulation
1       Europe  paris     city A-Regulated
2       Europe  paris     city G-Regulated
3       Europe  paris     city C-Regulated
7       Europe london     city A-Regulated
8       Europe london     city G-Regulated
9       Europe london     city C-Regulated
13 Netherlands   <NA>     <NA>        <NA>
14 New Zealand   <NA>     <NA>        <NA>
``````
``````merge(merge(merge(level.1, level.2, all = TRUE), level.3, all = TRUE), level.4, all = TRUE)
``````

## deleting combinations of vector from a vector of vectors

By : user3388632
Date : March 29 2020, 07:55 AM
it helps some times I am not sure if I understood the question correctly. Suppose you have
code :
``````v = { { 1,0} , {0,1} , {1,2}}
``````
``````v_final = { {1,0}, {1,2}}
``````
`````` std::unordered_set<std::unordered_set<int>> x;
x.insert( { 1,2} );
x.insert( { 2,1} );
``````