Sum data based on categorical criteria

[HABSaremyjam]

Hello,

I have a dataset with samples that require summation depending on where the sample was taken. The depth classes of the sample are "S", "D", "I," and "DS". Within the same transect (group), I would like to create a column that sums the volumes of D and DS.

For example, for transect stj38, the volumes with categories D (vol ~ 2.78) and DS (vol ~ 3.04) would sum to ~ 5.82 in the NEW_VOLUME column.

I'm guessing I would use the group_by() and summarize() or mutate() functions, as shown below, but I'm not sure where to go from there.

dtnew <- dt %>%
group_by(TRANSECT) %>%
mutate(NEW_VOLUME = function(x))

Or something like that. I don't know what syntax to use to describe how to sum the different DEPTH_CLASS categories.

Any help would be greatly appreciated.

Here's a snippet of my data:

dt <- structure(list(TRANSECT = c("stj17", "stj17", "stj38", "stj38", 
"stj38", "stj30", "stj30", "stj30", "stj23", "stj23"), SERIAL = c("166", 
"167", "177", "178", "179", "186", "187", "188", "195", "196"
), Volume_m3 = c(2.35845643690293, 14.7035018488167, 3.04633956433295, 
2.78838339154669, 4.63092748287711, 8.73365899290616, 9.51981113854047, 
6.00669373773715, 9.69178192039798, 9.188153202101), DEPTH_CLASS = c("S", 
"D", "DS", "D", "S", "DS", "D", "S", "DS", "D")), row.names = c(NA, 
10L), class = "data.frame")

Thanks so much!

[fcas80]

Is this what you want?

library(dplyr)
dt %>%
filter(DEPTH_CLASS != "S") %>%
group_by(TRANSECT) %>%
summarize(s = sum(Volume_m3))

A tibble: 4 x 2

TRANSECT s

1 stj17 14.7
2 stj23 18.9
3 stj30 18.3
4 stj38 5.83

[HABSaremyjam]

That actually works well with the mutate function, summarize seems to collapse all the rest of the data. Thank you so much for your help!