top_n: Select top (or bottom) n rows (by value)
In olascodgreat/samife: A Grammar of Data Manipulation

Description Usage Arguments Examples

This is a convenient wrapper that uses filter() and min_rank() to select the top or bottom entries in each group, ordered by wt.

1	top_n(x, n, wt)

x

a tbl() to filter

n

number of rows to return. If x is grouped, this is the number of rows per group. Will include more than n rows if there are ties.

If n is positive, selects the top n rows. If negative, selects the bottom n rows.

wt

(Optional). The variable to use for ordering. If not specified, defaults to the last variable in the tbl.

This argument is automatically quoted and later evaluated in the context of the data frame. It supports unquoting. See vignette("programming") for an introduction to these concepts.

df <- data.frame(x = c(10, 4, 1, 6, 3, 1, 1))
df %>% top_n(2)

# Negative values select bottom from group. Note that we get more
# than 2 values here because there's a tie: top_n() either takes
# all rows with a value, or none.
df %>% top_n(-2)

if (require("Lahman")) {
# Find 10 players with most games
# A little nicer with %>%
tbl_df(Batting) %>%
  group_by(playerID) %>%
  tally(G) %>%
  top_n(10)

# Find year with most games for each player
tbl_df(Batting) %>% group_by(playerID) %>% top_n(1, G)
}