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POCounting number of events underway at a timestamp
 

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    <p>I have a series of timestamps marking the beginning and end of certain events.</p> <pre><code>library(chron) start &lt;- structure(c(14246.3805439815, 14246.3902662037, 14246.3909606481, 14246.3992939815, 14246.4013773148, 14246.4034606481, 14246.4062384259, 14246.4069328704, 14246.4069328704, 14246.4097106481, 14246.4097106481, 14246.4104050926, 14246.4117939815, 14246.4117939815, 14246.4117939815, 14246.4145717593, 14246.4152546296, 14246.4152662037, 14246.4152662037, 14246.4159606481), format = structure(c("m/d/y", "h:m:s"), .Names = c("dates", "times")), origin = structure(c(1, 1, 1970), .Names = c("month", "day", "year")), class = c("chron", "dates", "times")) finish &lt;- structure(c(14246.436099537, 14246.4666550926, 14246.4083217593, 14246.4374884259, 14246.4847106481, 14246.4867939815, 14246.4305439815, 14246.4659606481, 14246.4520717593, 14246.9097106481, 14246.4930439815, 14246.4763773148, 14246.4326273148, 14246.4291550926, 14246.4187384259, 14246.9145717593, 14246.4395601852, 14246.4395717593, 14246.4395717593, 14246.4367939815), format = structure(c("m/d/y", "h:m:s"), .Names = c("dates", "times")), origin = structure(c(1, 1, 1970), .Names = c("month", "day", "year")), class = c("chron", "dates", "times")) events &lt;- data.frame(start, finish) head(event, 5) start finish 1 (01/02/09 09:07:59) (01/02/09 10:27:59) 2 (01/02/09 09:21:59) (01/02/09 11:11:59) 3 (01/02/09 09:22:59) (01/02/09 09:47:59) 4 (01/02/09 09:34:59) (01/02/09 10:29:59) 5 (01/02/09 09:37:59) (01/02/09 11:37:59) </code></pre> <p>I now wish to count how many events are underway at specific timestamps.</p> <pre><code>intervals &lt;- structure(c(14246.3958333333, 14246.40625, 14246.4166666667, 14246.4270833333, 14246.4375), format = structure(c("m/d/y", "h:m:s"), .Names = c("dates", "times")), origin = structure(c(1, 1, 1970), .Names = c("month", "day", "year")), class = c("chron", "dates", "times")) intervals [1] (01/02/09 09:30:00) (01/02/09 09:45:00) (01/02/09 10:00:00) (01/02/09 10:15:00) (01/02/09 10:30:00) </code></pre> <p>So the output I desire is as follows:</p> <pre><code> intervals count 1 (01/01/09 09:30:00) 3 2 (01/01/09 09:45:00) 7 3 (01/01/09 10:00:00) 19 4 (01/01/09 10:15:00) 18 5 (01/01/09 10:30:00) 12 </code></pre> <p>While the problem is trivial to solve programatically, I wish to accomplish this for 210,000 intervals and over 1.2 million events. My current approach involves leveraging the <code>data.table</code> package and the <code>&amp;</code> operator to check whether an interval lies between the start and end time of each event.</p> <pre><code>library(data.table) events &lt;- data.table(events) data.frame(intervals, count = sapply(1:5, function(i) sum(events[, start &lt;= intervals[i] &amp; intervals[i] &lt;= finish]))) </code></pre> <p>But considering the size of my data, this approach takes a very long time to run. Any advice on better alternatives to accomplish this in R?</p> <p>Cheers.</p>
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    1. USRahul Premraj
    1. USRahul Premraj
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      1. POCounting number of events underway at a timestamp
      1. USAnatoliy
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    1. COYou say you are using the `data.table` package. Care to show us the code you use? Your last line of code doesn't use `data.table` at all. You are simply using base R on a `data.frame`.
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      1. POCounting number of events underway at a timestamp
      1. USAndrie
    2. COThe data.table package allows you to '&' as an column index. The following throws an error: `events <- data.frame(events) data.frame(int, count = sapply(1:5, function(i) sum(events[, start <= int[i] & int[i] <= finish])))`
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      1. POCounting number of events underway at a timestamp
      1. USRahul Premraj
    3. COSubtle... Get it now. D'oh.
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      1. USAndrie
 

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