user2575429 user2575429 - 2 months ago 6
R Question

Efficient method to filter and add based on certain conditions (3 conditions in this case)

I have a data frame which looks like this

a b c d
1 1 1 0
1 1 1 200
1 1 1 300
1 1 2 0
1 1 2 600
1 2 3 0
1 2 3 100
1 2 3 200
1 3 1 0


I have a data frame which looks like this

a b c d
1 1 1 250
1 1 2 600
1 2 3 150
1 3 1 0


I am currently doing it
{

n=nrow(subset(Wallmart, a==i & b==j & c==k ))
sum=subset(Wallmart, a==i & b==j & c==k )
#sum
sum1=append(sum1,sum(sum$d)/(n-1))


}

I would like to add the 'd' coloumn and take the average by counting the number of rows without counting 0. For example the first row is (200+300)/2 = 250.
Currently I am building a list that stores the 'd' coloumn but ideally I want it in the format above. For example first row would look like

a b c d
1 1 1 250


This is a very inefficient way to do this work. The code takes a long time to run in a loop.
so any help is appreciated that makes it run faster. The original data frame has about a million rows.

Answer

You may try aggregate:

aggregate(d ~ a + b + c, data = df, sum)
#   a b c   d
# 1 1 1 1 500
# 2 1 3 1   0
# 3 1 1 2 600
# 4 1 2 3 300

As noted by @Roland, for bigger data sets, you may try data.table or dplyr instead, e.g.:

library(dplyr)
df %>%
  group_by(a, b, c) %>%
  summarise(
    sum_d = sum(d))

# Source: local data frame [4 x 4]
# Groups: a, b
# 
#   a b c sum_d
# 1 1 1 1   500
# 2 1 1 2   600
# 3 1 2 3   300
# 4 1 3 1     0

Edit following updated question. If you want to calculate group-wise mean, excluding rows that are zero, you may try this:

aggregate(d ~ a + b + c, data = df, function(x) mean(x[x > 0]))
#   a b c   d
# 1 1 1 1 250
# 2 1 3 1 NaN
# 3 1 1 2 600
# 4 1 2 3 150

df %>%
  filter(d != 0) %>%
  group_by(a, b, c) %>%
  summarise(
    mean_d = mean(d))

#   a b c mean_d
# 1 1 1 1    250
# 2 1 1 2    600
# 3 1 2 3    150

However, because it seems that you wish to treat your zeros as missing values rather than numeric zeros, I think it would be better to convert them to NA when preparing your data set, before the calculations.

df$d[df$d == 0] <- NA
df %>%
  group_by(a, b, c) %>%
  summarise(
    mean_d = mean(d, na.rm = TRUE))

#   a b c mean_d
# 1 1 1 1    250
# 2 1 1 2    600
# 3 1 2 3    150
# 4 1 3 1    NaN