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POMatching Columns, Creating Loop in R
 

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    <p>I have the following question:</p> <p>I have data frame which looks like this. I have prices, 3 X's and 2 R's.</p> <pre><code>Date Name Price Interest 01.02.10 X 120 0.2 01.02.10 R 120 0.3 01.02.10 X 130 0.8 01.02.10 X 140 0.4 01.02.10 R 130 0.2 etc. </code></pre> <p>I would like to tell R to look for pairs of X&amp;Rs with the same price, and delete the rest. So this should result: 2 X's and 2'Rs (in this case).</p> <pre><code>Date Name Price Interest 01.02.10 X 120 0.2 01.02.10 R 120 0.3 01.02.10 X 130 0.8 01.02.10 R 130 0.2 etc. </code></pre> <p>To make it clearer (hopefully): I have a lot of different prices for each date. Each row either has an X or an R in it. There are a lot of pairs on each date, i.e. for example X, Price = 120 &amp; R, Price = 120 on Date 1. But there are also Prices which only match one Name, for example there is a Price = 140 only for Name = X. So what i would like R to do is: check for machting Names for one Price (i.e. there exists the same Price for one X and one R) and delete the rest. What actually would result is the same number of X's and R's because I'm looking for pairs.</p> <p>I'm sorry not to be able to post something I tried. I just couldn't think of anything.</p> <p>Now, to the next problem: If the pairs are there, I would like to tell R to check each line. If the Name is X, I want it to calculate a new price, if not just print the existing price. I tried</p> <pre><code>xx &lt;- if(Name == "X"){Price + 100*interest} else print{Price} </code></pre> <p>but it didn't work.</p> <p>Thanks for help </p> <p>Cheers Dani</p>
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    1. COYou need to explain the logic of the first part better. "Look for pairs of Name and Price" doesn't make any sense to me. For the second part, you can use `ifelse()` instead of `if() ... else`, since the former is vectorized.
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    2. COOk thanks. I would like to look for matches for Prices and Names. So I have a lot of dates in my data frame, which either have the Name X or R. For each date, i also have price observations. Now, for each date, there should be exactly on pair of X&R for one price, e.g. Date 1, x , price = 120 and Date 1, r, price = 120. There are other observations that do not have a match, i.e. for example Date 1, x, price = 140 while there is NO Date 1, r, price = 140. I would like to tell R to check for matches (i.e X&R with same price on each date) and delete the rest. Is that clearer now? Thanks Shane
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      1. USDani
    3. COThat makes it a merge problem. You `merge` on Date and Name and then compare (test for equality) x.Price and y.Price.
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