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POAvoiding Loop with R using Apply (?)
 

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    <p>I'm trying to run apply a function to each row of a dataset. The function looks up matching rows in a second dataset and computes a similarity score for the product details passed to it.</p> <p>The function works if I just call it with test numbers but I can't figure out how to run it on all rows of my dataset. I've tried using apply but can't get it working.</p> <p>I'm going to be iterating different parameter settings to find those that best fit historical data so speed is important... meaning that a loop is out. Any help you can provide would be hugely appreciated.</p> <p>Thanks! Alan</p> <pre><code>GetDistanceTest &lt;- function(SnapshotDate, Cand_Type, Cand_Height, Cand_Age) { HeightParam &lt;- 1/5000 AgeParam &lt;- 1 Stock_SameType &lt;- HistoricalStock[!is.na(HistoricalStock$date) &amp; !is.na(HistoricalStock$Type) &amp; as.character(HistoricalStock$date)==as.character(SnapshotDate) &amp; HistoricalStock$Type==Cand_Type,] Stock_SameType$ED &lt;- (HeightParam*(Stock_SameType$Height - Cand_Height))^2 + (AgeParam*(Stock_SameType$Age - Cand_Age))^2 return(sqrt(sum(Stock_SameType$ED))) } HistoricalStock &lt;- HistoricalAQStock[,c(1, 3, 4, 5)] colnames(HistoricalStock) &lt;- c("date", "Age", "Height", "Type") Sales &lt;- AllSales[,c(2,10,11,25)] colnames(Sales) &lt;- c("date", "Age", "Height", "Type") GetDistanceTest("2010-04-01", 5261, 12, 7523) #works and returns a single number res1 &lt;- transform(Sales, ClusterScore=GetDistanceTest(date, Type, Height, Age)) # returns Error in `$&lt;-.data.frame`(`*tmp*`, "ED", value = c(419776714.528591, 22321257.0276852, : replacement has 4060 rows, data has 54 # also 4 warnings, one for each variable. e.g. 1: In as.character(HistoricalStock$date) == as.character(SnapshotDate) : longer object length is not a multiple of shorter object length res2 &lt;- apply(Sales, 1, GetDistanceTest, Sales$Type, Sales$Height, Sales$Age) # `$&lt;-.data.frame`(`*tmp*`, "ED", value = c(419648071.041523, 22325941.2704261, : replacement has 4060 rows, data has 13 # also same 4 warnings as res1 </code></pre>
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