从一个数据集中提取数据，在r中使用另一个

Question

I am trying to extract data from one data set (contains water quality data -- chlorophyll, dissolved oxygen, temp, etc), using information from another data set that contains tidal information (low tide times).

Background: It has recently come to my attention that due to hydrodynamics it will be best to only look at WQ data points measured at low tide, when I had previously just taken the daily average.

Is there a way I can extract specific WQ data based on if it aligns with date/time of the tidal data??? Caveats -- the times might not match up exactly, WQ data was measured every 15 minutes so I need the closest point(s) to the low tide time.

Answer 1

It is difficult to give the exact code without knowing the frequency of your tidal data. However, you can take a look at the following links, using which you could match the timestamps on both your datasets by rounding them off to the nearest hour/half hour/quarter hour (as the case may be):

1. rounding times to the nearest hour in R
2. Rounding time to nearest quarter hour

Hope this helps.