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POSelecting Specific Dates in R
 

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  1. POSelecting Specific Dates in R
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    <p>I am wondering how to create a subset of data in R based on a list of dates, rather than by a date range.</p> <p>For example, I have the following data set <code>data</code> which contains 3 years of 6-minute data. </p> <pre><code> date zone month day year hour minute temp speed gust dir 1 09/06/2009 00:00 PDT 9 6 2009 0 0 62 2 15 156 2 09/06/2009 00:06 PDT 9 6 2009 0 6 62 13 16 157 </code></pre> <p>I have used <code>breeze&lt;-subset(data, ws&gt;=15 &amp; wd&gt;=247.5 &amp; wd&lt;=315, select=date:dir)</code> to select the rows which meet my criteria for a sea breeze, which is fine, but what I want to do is create a subset of the days which contain those times that meet my criteria. </p> <p>I have used... </p> <pre><code>as.character(breeze$date) trimdate&lt;-strtrim(breeze$date, 10) breezedate&lt;-as.Date(trimdate, "%m/%d/%Y") breezedate&lt;-format(breezedate, format="%m/%d/%Y") </code></pre> <p>...to extract the dates from each row that meets my criteria so I have a variable called <code>breezedate</code> that contains a list of the dates that I want (not the most eloquent coding to do this, I'm sure). There are about two-hundred dates in the list. What I am trying to do with the next command is in my original dataset <code>data</code> to create a subset which contains only those days which meet the seabreeze criteria, not just the specific times.</p> <pre><code>breezedays&lt;-(data$date==breezedate) </code></pre> <p>I think one of my issues here is that I am comparing one value to a list of values, but I am not sure how to make it work. </p>
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    1. COA side-note: an alternative way to a date variable could be `as.Date(paste(year, month, day, sep = "-"))`. Or: `datetime <- as.POSIXct(date, format = "%m/%d/%Y %H:%M"); as.Date(datetime)`
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      1. USHenrik
    2. COOr: `trunc(as.POSIXct(date, format = "%m/%d/%Y %H:%M"), unit = "days")`
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