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Multiply column values per group in r

I have a data frame as following:

 id     weight     value
231      50         0.6
231      50         0.43
420      30         0.86
420      30         0.12

How can I multiply all values per each id and weight to have the following table:

id     weight     value
231     50       0.6*0.43
420     30       0.86*0.12
Solution

  • Use prod() to multiply all the values in its arguments.

    library(dplyr)

df %>%
  group_by(id, weight) %>%
  summarise(prod = prod(value))

# # A tibble: 2 x 3
# # Groups:   id [2]
#      id weight  prod
#   <int>  <int> <dbl>
# 1   231     50 0.258
# 2   420     30 0.103

    Or a base way

    aggregate(value ~ id + weight, df, prod)