*18*

You can use the following basic syntax to sum columns based on condition in R:

#sum values in column 3 where col1 is equal to 'A' sum(df[which(df$col1=='A'), 3])

The following examples show how to use this syntax in practice with the following data frame:

#create data frame df frame(conference = c('East', 'East', 'East', 'West', 'West', 'East'), team = c('A', 'A', 'A', 'B', 'B', 'C'), points = c(11, 8, 10, 6, 6, 5), rebounds = c(7, 7, 6, 9, 12, 8)) #view data frame df conference team points rebounds 1 East A 11 7 2 East A 8 7 3 East A 10 6 4 West B 6 9 5 West B 6 12 6 East C 5 8

**Example 1: Sum One Column Based on One Condition**

The following code shows how to find the sum of the points column for the rows where team is equal to ‘A’:

#sum values in column 3 (points column) where team is equal to 'A' sum(df[which(df$team=='A'), 3]) [1] 29

The following code shows how to find the sum of the rebounds column for the rows where points is greater than 9:

#sum values in column 4 (rebounds column) where points is greater than 9 sum(df[which(df$points > 9), 4]) [1] 13

**Example 2: Sum One Column Based on Multiple Conditions**

The following code shows how to find the sum of the points column for the rows where team is equal to ‘A’ *and* conference is equal to ‘East’:

#sum values in column 3 (points column) where team is 'A' and conference is 'East' sum(df[which(df$team=='A' & df$conference=='East'), 3]) [1] 29

Note that the **&** operator stands for “and” in R.

**Example 3: Sum One Column Based on One of Several Conditions**

The following code shows how to find the sum of the points column for the rows where team is equal to ‘A’ *or* ‘C’:

#sum values in column 3 (points column) where team is 'A'or'C' sum(df[which(df$team == 'A' | df$team =='C'), 3]) [1] 34

Note that the **|** operator stands for “or” in R.

**Additional Resources**

The following tutorials explain how to perform other common functions in R:

How to Sum Specific Columns in R

How to Sum Specific Rows in R

How to Calculate Sum by Group in R