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POMatrix algebra on a rolling subset of data in R
 

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  1. POMatrix algebra on a rolling subset of data in R
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    <p>I am a novice to R and have the following problem:</p> <p><strong>Data Input</strong>:</p> <p>I have a CSV with two columns like this:</p> <pre><code>1,10 2,20 3,30 4,40 5,50 ... N, M </code></pre> <p><strong>Problem:</strong></p> <pre><code>a) Read in the CSV b) Convert to a matrix c) Take 4 rows starting with the first row d) calculate the third column of elements as a simple square of the second column elements e) Calculate the sumproduct (value11*value12*value13 + value21*value22*value23 + value31*value32*value33 +value41*value42*value43) f) Do this until the end of the dataset </code></pre> <p>Outcome:</p> <p>The result for the first two matrices should be as follows:</p> <p><strong>First matrix:</strong></p> <p>Start with the first row, select four rows.</p> <p>Step 1</p> <pre><code>1,10 2,20 3,30 4,40 </code></pre> <p>Step 2 (add the 3rd column as a square of the second column value)</p> <pre><code>1,10,100 2,20,400 3,30,900 4,40,1600 </code></pre> <p>Step 3 (calculate the sumproduct) (1*10*100 + 2*20*400 +3*30*900 + 4*40*1600) == 354.000</p> <p><strong>Second matrix:</strong></p> <p>Proceed with the second row and take the next 4 rows</p> <p>Step 1</p> <pre><code>2,20 3,30 4,40 5,50 </code></pre> <p>Step 2 (add the 3rd column as a square of the second column value)</p> <pre><code>2,20,400 3,30,900 4,40,1600 5,50,2500 </code></pre> <p>Step 3 (calculate the sumproduct)</p> <pre><code>(2*20*400 +3*30*900 + 4*40*1600 + 5*50*2500) == 978.000 </code></pre> <p><strong>N matrix</strong> Do steps 1 to 3 until the end of the dataset</p> <p><strong>RESULT</strong> </p> <p>The result should be the list of sumproducts:</p> <pre><code>354.000, 978.000, ..., N </code></pre> <p>Thank you!</p>
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    1. USuser1766682
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    1. COI do not believe that you are unable to solve at least some checkpoints in your problem description by doing some research, eg. reading basic introductions and tutorials.
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      1. POMatrix algebra on a rolling subset of data in R
      1. USRoland
    2. COHi Roland, I solved some of the checkpoints. My problem is how to define the four row chunks of the data as a matrix and do it until the end of the dataset. I event managed to do it with a For loop but I think there should be a better way to do it as a simple loop.
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      1. POMatrix algebra on a rolling subset of data in R
      1. USuser1766682
    3. COYou're close. Think about how you would subset your rows based on an index. You can probably do this in a number of ways, but a `for` loops would be one intuitive approach.
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      1. POMatrix algebra on a rolling subset of data in R
      1. USRoman Luštrik
 

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