How to sum data.frame column values?

r dataframe sum aggregate-functions
User picture User · Mar 13, 2012 · Viewed 364.1k times · Source

I have a data frame with several columns; some numeric and some character. How to compute the sum of a specific column? I’ve googled for this and I see numerous functions (sum, cumsum, rowsum, rowSums, colSums, aggregate, apply) but I can’t make sense of it all.

For example suppose I have a data frame people with the following columns

people <- read(
  text = 
    "Name Height Weight
    Mary 65     110
    John 70     200
    Jane 64     115", 
  header = TRUE
)
…

How do I get the sum of all the weights?

Answer

mathematical.coffee picture mathematical.coffee · Mar 13, 2012

You can just use sum(people$Weight).

sum sums up a vector, and people$Weight retrieves the weight column from your data frame.

Note - you can get built-in help by using ?sum, ?colSums, etc. (by the way, colSums will give you the sum for each column).

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