Sum data in one column based on condition in another column

[lisahildy]

Hi R gurus! I need some help wrangling some data (screenshot attached to this post). Apologies, I don't even know where to begin so I don't have any R code yet...

I have a data frame of 1330 observations and I would like to sum the average column in chunks based on values in the m_off_ground column. Specifically, when a 0 occurs in the m_off_ground column, I want the sum calculation to 'restart' in the average column. Unfortunately, the 0s do not occur at regular intervals.
Furthermore, I'd like to create a column 'no_frames' which will tell me the number of columns/values included in each sum calculation.
So, the first one would be the sum of rows 2-11 in the average column (since there is a 0 in row 12 in the m_off_ground column) and the no_frames would equal 10.

I know there must be some for loop way to do this, or perhaps even a dplyr way but as a still relatively new R user, my brain can't wrap itself around how to do this....

Thanks so much for any help or advice!

[FJCC]

It looks to me like another way to express what you want is that you want a sum of the average column for each value of the station column. Is that true?

[lisahildy]

Hi FJCC,

while that is true, I sample the same 12 stations for 1 month, so those station names are repeated throughout the data frame for ~20 different dates. Sorry, I should have included that in my original post.

Thanks,

Lisa

[FJCC]

So you want to do the calculation for each station on each date? The reason I am pushing on this is that it is far easier to do such calculations by taking advantage of labels in other columns rather than trying to step down a column and look at patterns of values.

[lisahildy]

Yes, you're right! It would be summing the average column for each station on each date. I don't know why I didn't think of that....
Also (sorry to add another layer to this) - would there be a way to "grab" the last value in the m_off_ground column per station per date. So for the first one that would be 7.0899.

[FJCC]

If the last value is always the largest, I would do your calculations like this (naming your data frame DF)

Stats <- DF %>% group_by(station, date) %>% 
     summarize(SumAvg = sum(average, na.rm = TRUE), MaxOffGrd = max(m_off_ground), NumFrames = n())

[lisahildy]

Wow, thank you so, so much FJCC! Such an easy and elegant way of doing that. Thanks for all your help