排除R中的特定时间段 [英] Exclude specific time periods in R
问题描述
我是R的初学者，并尝试在某些时间段内搜索数据提取，但似乎找不到任何东西。
I'm a beginner with R and have tried searching for data extraction for certain time periods but can't seem to find anything.
我有一个时间序列连续数据以10分钟间隔测量，持续5个月。为简单起见，数据可以在两列中提供如下：
I have a time series of continuous data measured at 10 minute intervals for a period of five months. For simplicity's sake, the data is available in two columns as follows:
Timestamp Temp.Diff
2/14/2011 19:00 -0.385
2/14/2011 19:10 -0.535
2/14/2011 19:20 -0.484
2/14/2011 19:30 -0.409
2/14/2011 19:40 -0.385
2/14/2011 19:50 -0.215
...和在接下来的五个月里，我已经使用as.POSIXct（）读入了Timestamp列。
... And it goes on for the next five months. I have read the Timestamp column using as.POSIXct() into R.
假设只有一天的某些时间对我有兴趣（例如从中午12点到下午3点），我想要排除当天的其他几个小时，或者只是提取3个小时，但仍然按照数据流顺序（即时间序列）。我明白，如果您知道行号，您可以轻松地对数据进行子集，但是由于这是一个更大的数据集，是否有一种方式来编码R，以便自动识别我查看的时间段？
Assuming that only certain times of the day are of interest to me, (e.g. from 12 noon to 3 PM), I would like either like to exclude the other hours of the day, OR just extract those 3 hours but still have the data flow sequentially (i.e. in a time series). I understand that you can easily subset data if you know the row numbers, but as this is a much larger dataset, is there a way to code R so it automatically recognises the time period I'm looking at?
推荐答案
你似乎知道基本的想法，但只是错过了细节。正如你所提到的，我们只是将Timestamps转换成POSIX对象，然后将子集。
You seem to know the basic idea, but are just missing the details. As you mentioned, we just transform the Timestamps into POSIX objects then subset.
lubridate解决方案
最简单的方法可能是使用lubridate。首先加载包：
The easiest way is probably with lubridate. First load the package:
library(lubridate)
接下来转换时间戳：
##*m*onth *d*ay *y*ear _ *h*our *m*inute
d = mdy_hm(dd$Timestamp)
然后我们选择我们想要的。在这种情况下，我希望在下午7点半之后的任何日期（不管一天）：
Then we select what we want. In this case, I want any dates after 7:30pm (regardless of day):
dd[hour(d) == 19 & minute(d) > 30,]
/ strong>
Base R solution
首先创建一个上限：
lower = strptime("2/14/2011 19:30","%m/%d/%Y %H:%M")
下一步将POSIX对象中的时间戳变换：
Next transform the Timestamps in POSIX objects:
d = strptime(dd$Timestamp, "%m/%d/%Y %H:%M")
最后，一点数据帧子集：
Finally, a bit of dataframe subsetting:
dd[format(d,"%H:%M") > format(lower,"%H:%M"),]
感谢plannapus最后一部分
上述示例的数据：
dd = read.table(textConnection('Timestamp Temp.Diff
"2/14/2011 19:00" -0.385
"2/14/2011 19:10" -0.535
"2/14/2011 19:20" -0.484
"2/14/2011 19:30" -0.409
"2/14/2011 19:40" -0.385
"2/14/2011 19:50" -0.215'), header=TRUE)
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