我将用一个例子来说明我的问题.
样本数据:
df <- data.frame(ID = c(1, 1, 2, 2, 3, 5), A = c("foo", "bar", "foo", "foo", "bar", "bar"), B = c(1, 5, 7, 23, 54, 202))
df
ID A B
1 1 foo 1
2 1 bar 5
3 2 foo 7
4 2 foo 23
5 3 bar 54
6 5 bar 202
我想做的是,通过ID,总结出B的和,当A是"foo"时,B的和.我可以通过以下几个步骤来实现:
require(magrittr)
require(dplyr)
df1 <- df %>%
group_by(ID) %>%
summarize(sumB = sum(B))
df2 <- df %>%
filter(A == "foo") %>%
group_by(ID) %>%
summarize(sumBfoo = sum(B))
left_join(df1, df2)
ID sumB sumBfoo
1 1 6 1
2 2 30 30
3 3 54 NA
4 5 202 NA
然而,我正在寻找一种更优雅/更快的方法,因为我正在处理sqlite中10gb+的内存不足数据.
require(sqldf)
my_db <- src_sqlite("my_db.sqlite3", create = T)
df_sqlite <- copy_to(my_db, df)
我想用mutate
来定义一个新的Bfoo
列:
df_sqlite %>%
mutate(Bfoo = ifelse(A=="foo", B, 0))
不幸的是,这在数据库端不起作用.
Error in sqliteExecStatement(conn, statement, ...) :
RS-DBI driver: (error in statement: no such function: IFELSE)