[R] Create a data subset

[MarySR]

Hello,
I want to select same data of a data frame that has information of fish
catches:

     catch, vessel, trip, day, month, year

where trip is the fishing operation number done in each day by each vessel,
i.e. for each day, any vesel can have several register of catch
corresponding to each operation.
>From this data frame I want to do:
1. Add the catches of all trip by vessel and day; then
2. Select rows corresponding to vessels that appear more than 120 days at
the year; then
3. Select rows corresponding to vessels that appear mode than 15 years
Does anyone know how to do that in R?

Thank you in advanced

Maria

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