If I have two lists:
a:1 2 3 4;
b:10 20 30 40;
I want to sum the product of the two lists within a window of 2. So the result set should be:
10 50 130 250
For example, to get the result of 130 it would be (2*20)+(3*30) = 130
sums 2 mavg '(a*b)
seems to get me part way there, but the window of 2 isn't being applied. I've tried experimenting with sum, sums, sum each, wavg, mavg, etc. and I am completely stuck. Could anyone help? Thanks!
This line should work for you:
2 msum a*b
as demonstrated here:
q)a:1 2 3 4
q)b:10 20 30 40
q)2 msum a*b
10 50 130 250
For more information about the keyword msum, you could check out the Kx Reference page:
https://code.kx.com/wiki/Reference/msum
Hope that helps!
Alternatively you could use the adverb each prior:
q)+':[a*b]
However this will only work with a window size of 2 and if your data contains null values this needs to be padded with 0:
q)+':[0^a*b2]
On a positive note it is faster than using msum in this situation.
q)\ts:1000000 +':[0^a*b2]
940 1264
q)\ts:1000000 2 msum a*b2
1556 1104
Related
I have a table, which is :
t:([]a:1 3 2 1 2 3 3 2 1;b:10 20 30 40 50 60 70 80 90;c:100 200 300 400 500 600 700 800 900)
And I want all c to be 0 where a is equal to 2, and all be to be 0 where a is equal to 1.
Currently I have these two codes:
t:update b:0 from t where a=1
t:update c:0 from t where a=2
My question is how to combine these two lines of codes into one. Because I am working on a table which is far bigger than this simple example and it will take me a lot of rows of codes to do all the updates, which is too long.
You can use vector conditional for this:
update b:?[a=1;0;b], c:?[a=2;0;c] from t
I have three tables (actually temp tables, each the result of other queries), with very similar data sets; I need to "condense", for lack of a better term, and my limited SQL knowledge is stopping me.
For example, we have Budgets by Code, Estimates by Code, and Actuals by Code. Not all possible values for Code exist in any of the three, nor even in another accessible table.
Budgets
1 $13
2 $22
4 $44
7 $71
Estimates
1 $14
4 $49
5 $55
Actuals
2 $21
3 $33
5 $57
7 $70
What I want:
Code Bgt Est Act
1 13 14 0
2 22 0 21
3 0 0 33
4 44 49 0
5 0 55 57
7 71 0 70
(I don't have to have 0 when there's no value, that's just for illustrative purposes.)
I just have no idea how to approach this - any help appreciated!
Try using Full Outer Join, In your case query will look like -
Select ISNULL(Bgt.Code,ISNULL(EST.Code,Act.Code)) AS Code,
ISNULL(Bgt.Budget,0) AS Bgt,
ISNULL(Est.Estimate,0) AS Est,
ISNULL(Act.Actual,0) AS Bgt
FROM Budget Bgt
FULL OUTER JOIN Estimates Est ON Est.Code=Bgt.Code
FULL OUTER JOIN Actuals Act ON Act.Code=bgt.Code
I want to calculate the sum of the elements surrounding a given element in a matrix. So far, I have written these lines of code:
for i=1:m,
rij(1:n)=0
for j=1:n,
alive = tijdelijk(i-1,j)+tijdelijk(i+1,j)+tijdelijk(i-1,j-1)+tijdelijk(i+1,j-1)+tijdelijk(i,j+1)+tijdelijk(i,j-1)+tijdelijk(i-1,j+1)+tijdelijk(i+1,j+1)
This results in an error because, for example, i-1 becomes zero for i=1. Anyone got an idea how to do this without getting this error?
You can sum the elements via filtering. conv2 can be used for this manner.
Let me give an example. I create a sample matrix
>> A = reshape(1:20, 4, 5)
A =
1 5 9 13 17
2 6 10 14 18
3 7 11 15 19
4 8 12 16 20
Then, I create a filter. The filter is like a mask where you put the center on the current cell and the locations corresponding to the 1's on the filter are summed. For eight-connected neighbor case, the filter should be as follows:
>> B = [1 1 1; 1 0 1; 1 1 1]
B =
1 1 1
1 0 1
1 1 1
Then, you simply convolve the matrix with this small matrix.
>> conv2(A, B, 'same')
ans =
13 28 48 68 45
22 48 80 112 78
27 56 88 120 83
18 37 57 77 50
If you want four-connected neighbors, you can make the corners of your filter 0. Similarly, you can design any filter for your purpose, such as for averaging all neighbors instead of summing them.
For details, please see the convolution article in Wikipedia.
Two possibilities : change the limits of the loops to i=k:(m-k) and j=k:(n-k) or use blkproc
ex :
compute the 2-D DCT of each 8-by-8 block
I = imread('cameraman.tif');
fun = #dct2;
J = blkproc(I,[8 8],fun);
imagesc(J), colormap(hot)
There are lots of things you can do at the edges. Which you do depends very specifically on your problem and is different from usage case to usage case. Typical things to do:
If (i-1) or (i+1) is out of range, then just ignore that element. This is equivalent to zero padding the matrix with zeros around the outside and adjusting the loop limits accordingly
Wrap around the edges. In other words, for an MxN matrix, if (i-1) takes you to 0 then instead of taking element (i-1, j) = (0, j) you take element (M, j).
Since your code mentions "your teacher" I'd guess that you can ask what should happen at the edges (or working it out in a sensible manner may well be part of the task!!).
I am doing some simulations studies and for initial stuides I am trying to simulate 100 gas particles and then grouping of these gas particles in 5 groups randomly for 10 or 100 times (non zero values in any groups). after that i have to find the group with highest particle and the number.
for example
100 gas particles
1 2 3 4 5(groups) Total particle group/Highest number
20|20|20|20|20 100 1-2-3-4-5/20
70|16|04|01|09 100 1/70
18|28|29|10|15 100 3/29
.
.
etc
i have used this to generate 5 random numbers for a single time
for i=1:1
randi([1,100],1,5)
end
ans =
50 41 9 60 88
but how will i find the highest number and group?
Use the max function :
a = [50 41 9 60 88];
[C,I] = max(a)
C should be equal to 88 and I to 4.
For the special case of equality (first line in your code), you have to read the documentation to see the result of max. I think the index returned will be the first max.
I have the following array
a = [ 1 10 3 4 68 2 34 8 10 ]
And I need to divide each number (/2) if this number is higher than 9.
This means that 1 has not to be divided, and 10 has to be divided (/2)
The resulting array should be:
a = [ 1 5 3 4 34 2 17 8 5 ]
I have to do it without using a FOR function. So I tried with this:
a = a./2;
This divides every number of the array, and I as told you before, I want to divide only the ones higher than 9.
Can anyone tell me how can I do it? Add a 'if whatever>5' in that statement or something?
Thanks in advance
Use logical indexing for both dividing only the numbers that meets your criterion and for assigning the result to those specific indices.
a = [ 1 10 3 4 68 2 34 8 10 ];
a(a>9) = a(a>9) ./ 2