Question

I have this dataframe:

> names(events)
 [1] "EID"    "X"      "Y"      "trip"   "tow"    "catch"  "effort" "depth" 
 [9] "season" 

Where some of my unique ID “EID” appears more than once in 162 cases.

> length(events$EID)-length(unique(events$EID))
[1] 162

I would like to combined each replicate EID together and sum their “catch”.
I’ve been trying a few things with the plyr package… but can’t find a rather straightforward command.

Any tips would be much appreciated!
Thank you very much!

Answer 1

Here is an example that should get you started:

library(plyr)

n = 100

# Simulate data
set.seed(12345)
EID   = factor(sample(10, n, replace=T))
catch = runif(n)
data  = data.frame(EID, catch)

# Sum catch by EID
ddply(data, 'EID', function(x) data.frame(catch.sum = sum(x$catch)))

> ddply(data, 'EID', function(x) data.frame(catch.sum = sum(x$catch)))
   EID catch.sum
1    1  6.041294
2    2  4.889522
3    3  2.466826
4    4  9.633270
5    5  5.673484
6    6  3.389666
7    7  6.572664
8    8  8.646577
9    9  4.056461
10  10  5.933441