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POPuzzling behavior in simple logical test applied to vector of values
 

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  1. POPuzzling behavior in simple logical test applied to vector of values
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    <p>Ok, this has me absolutely perplexed and worried- As part of a routine, I have been classifying individual observations of variables as <code>TRUE</code> or <code>FALSE</code> based on whether their values are above or below/equal to the median value. However, I have been getting a behavior in R that is largely unexpected from performing this simple test.</p> <p>So take this set of observations:</p> <pre><code>data=c(0.6666667, 0.8333, 0.6666667, 0.8333, 0.8333, 0.75, 0.9999, 0.7499667, 0.25, 0.6666667, 0.1667, 0.7499667, 0.5, 0.2500333, 0.3333667, 0.0834, 0.0001, 0.2500333, 0.8333, 0.9999, 0.9999, 0.2500333, 0.2500333, 0.3333667, 0.9166, 0.5, 0.2500333, 0.4166667, 0.0001, 0.1667333, 0.6666333, 0.0834, 0.1667, 0.6666333, 0.9166, 0.1667, 0.7499333, 0.9166, 0.9166, 0.9166, 0.7499667, 0.7499667, 0.4166667, 0.5, 0.2500333, 0.9166, 0.6666667, 0.1667333, 0.25, 0.0001, 0.3333667, 0.0001, 0.25, 0.0834, 0.9999, 0.0834, 0.1667, 0.5, 0.2500333, 0.3333667, 0.9166, 0.9166, 0.8333, 0.9166, 0.75, 0.0834, 0.4166667, 0.5, 0.0001, 0.9999, 0.8333, 0.6666667, 0.9166) </code></pre> <p>For me to classify these values, I did:</p> <pre><code>data_med=median(data) quant_data=data quant_data[quant_data&gt;data_med]="High" quant_data[quant_data&lt;=data_med]="Low" </code></pre> <p>I know there are 1 gazillion ways of doing this more efficiently, but what has me worried is that the output from this does not make sense. Since there are no <code>NaN</code>s on the set and the test is all inclusive (<code>&gt;</code> or <code>&lt;=</code>), I should end up with a list of only <code>TRUE</code>/<code>FALSE</code> values, but instead I get:</p> <pre><code>[1] "High" "High" "High" "High" "High" "High" "High" "High" "Low" "High" "Low" "High" "Low" "Low" "Low" "Low" "1e-04" [18] "Low" "High" "High" "High" "Low" "Low" "Low" "High" "Low" "Low" "Low" "1e-04" "Low" "High" "Low" "Low" "High" [35] "High" "Low" "High" "High" "High" "High" "High" "High" "Low" "Low" "Low" "High" "High" "Low" "Low" "1e-04" "Low" [52] "1e-04" "Low" "Low" "High" "Low" "Low" "Low" "Low" "Low" "High" "High" "High" "High" "High" "Low" "Low" "Low" [69] "1e-04" "High" "High" "High" "High" </code></pre> <p>See the "1e-04"s? What is even stranger, let's pick value 69, one of the ones that return odd values:</p> <pre><code>data[69] &gt;1e-04 </code></pre> <p>If I test this value alone, I get what I expected to get:</p> <pre><code>data[69]&lt;=data_med TRUE </code></pre> <p>Can someone explain this behavior? It just seems downright dangerous... </p>
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    1. USLucas Fortini
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      1. POPuzzling behavior in simple logical test applied to vector of values
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    1. CORemove this line: `quant_data=data` and use `data` instead of `quant_data` in the `[. < data_med`, then try your code. You're assigning `High` to a *numeric vector* which replaces it to a `character vector`. Inspect your current output after assigning `High` to understand better what's happening.
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      1. USArun
    2. COA relatively better way to accomplish this task is using `ifelse` for ex: `quant_data <- ifelse(data > data_med, "High", "Low")`
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      1. USArun
    3. COWhy the down-vote?
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      1. POPuzzling behavior in simple logical test applied to vector of values
      1. USArun
 

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