Summing rows based on specific factor combinations

Question

This is probably a silly question, but I have read through Crawley's chapter on dataframes and scoured the internet and haven't yet been able to make anything work.

Here is a sample dataset similar to mine:

> data<-data.frame(site=c("A","A","A","A","B","B"), plant=c("buttercup","buttercup",
"buttercup","rose","buttercup","rose"), treatment=c(1,1,2,1,1,1), 
plant_numb=c(1,1,2,1,1,2), fruits=c(1,2,1,4,3,2),seeds=c(45,67,32,43,13,25))
> data
  site     plant treatment plant_numb fruits seeds
1    A buttercup         1          1      1    45
2    A buttercup         1          1      2    67
3    A buttercup         2          2      1    32
4    A      rose         1          1      4    43
5    B buttercup         1          1      3    13
6    B      rose         1          2      2    25  

What I would like to do is create a scenario where "seeds" and "fruits" are summed whenever unique site & plant & treatment & plant_numb combinations exist. Ideally, this would result in a reduction of rows, but a preservation of the original columns (ie I need the above example to look like this:)

  site     plant treatment plant_numb fruits seeds
1    A buttercup         1          1      3   112
2    A buttercup         2          2      1    32
3    A      rose         1          1      4    43
4    B buttercup         1          1      3    13
5    B      rose         1          2      2    25

This example is pretty basic (my dataset is ~5000 rows), and although here you only see two rows that are required to be summed, the numbers of rows that need to be summed vary, and range from 1 to ~45.

I've tried rowsum() and tapply() with pretty dismal results so far (the errors are telling me that these functions are not meaningful for factors), so if you could even point me in the right direction, I would greatly appreciate it!

Thanks so much!

Answer 1

Hopefully the following code is fairly self-explanatory. It uses the base function "aggregate" and basically this is saying for each unique combination of site, plant, treatment, and plant_num look at the sum of fruits and the sum of seeds.

# Load your data
data <- data.frame(site=c("A","A","A","A","B","B"), plant=c("buttercup","buttercup",
"buttercup","rose","buttercup","rose"), treatment=c(1,1,2,1,1,1), 
plant_numb=c(1,1,2,1,1,2), fruits=c(1,2,1,4,3,2),seeds=c(45,67,32,43,13,25)) 

# Summarize your data
aggregate(cbind(fruits, seeds) ~ 
      site + plant + treatment + plant_numb, 
      sum, 
      data = data)
#  site     plant treatment plant_numb fruits seeds
#1    A buttercup         1          1      3   112
#2    B buttercup         1          1      3    13
#3    A      rose         1          1      4    43
#4    B      rose         1          2      2    25
#5    A buttercup         2          2      1    32

The order of the rows changes (and it sorted by site, plant, ...) but hopefully that isn't too much of a concern.

An alternative way to do this would be to use ddply from the plyr package.

library(plyr)
ddply(data, .(site, plant, treatment, plant_numb), 
      summarize, 
      fruits = sum(fruits), 
      seeds = sum(seeds))
#  site     plant treatment plant_numb fruits seeds
#1    A buttercup         1          1      3   112
#2    A buttercup         2          2      1    32
#3    A      rose         1          1      4    43
#4    B buttercup         1          1      3    13
#5    B      rose         1          2      2    25