Suppose I have 121 elements and want to get all combinations of 4 elements taken at a time, i.e. 121c4.
Since combnk(1:121, 4) takes a lot of time, I want to go for 2% of that combination by providing:
z = 1:50:length(121c4(:, 1))
For example: 1st row, 5th row, 100th row and so on, up to 121c4, picking only those rows from a 121c4 matrix without generating the complete combination (it's consuming too much for large numbers like 625c4).
If you haven't defined an ordering on the combinations, why not just use
randi(121,p,4)
where p is the number of combinations you want in your set ? With this approach you may, or may not, want to replace duplicates.
If you have defined an ordering on the combinations, tell us what it is.
Related
On one sheet, I have account code and in the cell next to it, I need to look up the account code on the next sheet to average the cost excluding those cells that are zero in col. b from the average calculation.
The answer for London should be: £496.33 but having tried various sumifs / countifs I cannot get it to work.
You probably need COUNTIFS which -- similar to the SUMIFS you are already using -- allows to define multiple critera and ranges.
So, if the column R contains the values, you want to build the average upon, and the column H in the respective row must equal $B$28 to be included in the sum, the respective COUNTIFS looks as follows
=SUMIFS('ESL Info'!$R:$R,'ESL Info'!H:H,$B$28)/COUNTIFS('ESL Info'!$H:$H,$B$28, 'ESL Info'!$R:$R, "<>0")
ie additionally to the value in the H-column to equal B28 it also requires the value R-column (ie the actual number you are summing up) to be different from 0
You could also add the same criteria 'ESL Info'!$R:$R, "<>0" to your SUMIFS, but that isn't necessary, because a 0 doesn't provide anything to you sum, thus it doesn't matter if it's included in the sum or not ...
And depending on the Excel version you are using, you may even have the AVERAGEIFS function available, which does exactly what you want
=AVERAGEIFS('ESL Info'!$R:$R,'ESL Info'!$H:$H;$B$28,'ESL Info'!$R:$R,"<>0")
For example,
A=[a,b,c,d]
B=[1,2,3,4]
my question is: how to generate all possible ways to merge A and B, such that in the new list we can have a appears before b, b appears before c,etc., and 1 appears before 2, 2 appears before 3,etc.?
I can think of one implementation:
We choose 4 slots from 8,then for each possible selection, there are 2 possible ways--A first or B first.
I wonder is there a better way to do this?
EDIT:
I've just learned a more intuitive way--use recursion.
For each spot, there are two possible cases, either taken from A or taken from B; keep recursing until A or B is empty, and concatenate the remaining.
If the relative order is different than what constitutes a sorted list (I assume it is, because otherwise it would not be a problem), then you need to formalize the initial order. Multiple ways to do that. the easiest being remembering the index of each element in each list. Example: valid position for a is 1 in the first array [...]
Then you could just go ahead and join the lists, then generate all the permutations of elements. Any valid permutation is one that keeps the order relationship of the new indexes with the order you have stored
Example of one valid permutation array
a12b3cd4
You can know and check that this is valid permutation because the index of element 'a' is smaller than the index of b, and so on. and you know the indexes must be smaller because this is what you have formulated at the first step
Similarly an invalid permutation array is
ba314cd2
same way of checking
I am sorry for this complicated problem, but, I will try my best to explain myself.
This is basically a Hidden Markov Model question. I have two columns of data. The data in these two columns are independent of each other, however, together represent a specific movement which can be character-coded. I assign a character in 3rd column by putting conditions on column1 and column2 entry. Note: the characters are finite (~10-15).
For example:-
if (column1(i)>0.5) && (column2(i)<15)
column3(i)='D';
I end up with a string something like this
AAAAADDDDDCCCCCFFFFAAAACCCCCFFFFFFDDD
So, each of the character gets repeated but not of constant lengths (e.g first time A's appear 5 times while second time A's appear 4 times only).
Now, let us take the first chunk of A's (AAAAA), each A containing an ordered pair of column1 and column2 values. Now, comparing with the second chunk of A's (AAAA), the values of column1 and column2 should be similar to those of first chunk. Usually, the values in each columns would be either increasing or decreasing or constant throughout a chunk. And the values of the columns in both chunks should be similar. For example, column1 goes from -1 to -5 in 5 unequal samples but in second chunk it goes from -1.2 to -5.1 in 4 unequal steps.
What I want is a fitting of a probability distribution over column1 and column2 values (independently) for each set of repeated characters (e.g. for A's and then D's then C's then F's and then again A's).
And the final goal is following:-
given n elements in column1, column2, column3, I want to predict what is (n+1) element is going to be in column 3, how many times it is going to repeat itself (with probability e.g. 70% chance it is going to repeat itself 4 times and 20% chance it is going to repeat itself 5 times). Also, what is the probability distribution of column1 and column2 is going to be for the predicted character.
Please feel free to ask questions if I fail to explain it well.
I have a 161*32 matrix (labelled "indpic") in MATLAB and I'm trying to find the frequency of a given number appearing in a row. So I think that I need to analyse each row separately for each value, but I'm incredibly unsure about how to go about this (I'm only new to MATLAB). This also means I'm incredibly useless with loops and whatnot as well.
Any help would be greatly appreciated!
If you want to count the number of times a specific number appears in each row, you can do this:
sum(indpic == val, 2)
where indpic is your matrix (e.g image) and val is the desired value to be counted.
Explanation: checking equality of each element with the value produces a boolean matrix with "1"s at the locations of the counted value. Summing each row (i.e summing along the 2nd dimension results in the desired column vector, where each element being equal to the number of times val is repeated in the corresponding row).
If you want to count how many times each value is repeated in your image, this is called a histogram, and you can use the histc command to achieve that. For example:
histc(indpic, 1:256)
counts how many times each value from 1 to 256 appears in image indpic.
Like this,
sum(indpic(rownum,:) == 7)
obviously change 7 to whatever.
You can just write
length(find(indpic(row_num,:)==some_value))
and it will give you the number of elements equal to "some_value" in the "row_num"th row in matrix "indpic"
I have created a vector containing zeros and 1's using the following command in a for loop.
G(:,i)=rand(K,1)<rand;
Since this is part of a larger problem at a particular stage I need to count the number of 1's that are present in each column.
I have tried to find the count using a for loop which is very messy and takes too long.
I found that histc can be used for this but I get an error
histc(G(:,1),1)
First input must be non-sparse numeric array.
Is there a better way to do this or am I missing something here ?
If you have a matrix G containing zeroes and ones, and you want to know how many ones are in each column, all you need is SUM:
nZeroes = sum(G);
This will give you a vector containing a total for each column in G.