Pass SQL functions in dplyr filter function on database - sql

Question

I'm using dplyr's automatic SQL backend to query subtable from a database table. E.g.
my_tbl <- tbl(my_db, "my_table")
where my_table in the database looks like
batch_name value
batch_A_1 1
batch_A_2 2
batch_A_2 3
batch_B_1 8
batch_B_2 9
...
I just want the data from batch_A_#, regardless of the number.
If I were writing this in SQL, I could use
select * where batch_name like 'batch_A_%'
If I were writing this in R, I could use a few ways to get this: grepl(), %in%, or str_detect()
# option 1
subtable <- my_tbl %>% select(batch_name, value) %>%
filter(grepl('batch_A_', batch_name, fixed = T))
# option 2
subtable <- my_tbl %>% select(batch_name, value) %>%
filter(str_detect(batch_name, 'batch_A_'))
All of these give the following Postgres error: HINT: No function matches the given name and argument types. You might need to add explicit type casts
So, how do I pass in SQL string functions or matching functions to help make the generated dplyr SQL query able to use a more flexible range of functions in filter?
(FYI the %in% function does work, but requires listing out all possible values. This would be okay combined with paste to make a list, but does not work in a more general regex case)

Answer 1

A "dplyr-only" solution would be this
tbl(my_con, "my_table") %>%
filter(batch_name %like% "batch_A_%") %>%
collect()
Full reprex:
suppressPackageStartupMessages({
library(dplyr)
library(dbplyr)
library(RPostgreSQL)
})
my_con <-
dbConnect(
PostgreSQL(),
user = "my_user",
password = "my_password",
host = "my_host",
dbname = "my_db"
)
my_table <- tribble(
~batch_name, ~value,
"batch_A_1", 1,
"batch_A_2", 2,
"batch_A_2", 3,
"batch_B_1", 8,
"batch_B_2", 9
)
copy_to(my_con, my_table)
tbl(my_con, "my_table") %>%
filter(batch_name %like% "batch_A_%") %>%
collect()
#> # A tibble: 3 x 2
#> batch_name value
#> * <chr> <dbl>
#> 1 batch_A_1 1
#> 2 batch_A_2 2
#> 3 batch_A_2 3
dbDisconnect(my_con)
#> [1] TRUE
This works because any functions that dplyr doesn't know how to
translate will be passed along as is, see
?dbplyr::translate\_sql.
Hat-tip to #PaulRougieux for his recent comment
here

Answer 2

Using dplyr
Get the table batch_name from the database as dataframe and use it for further data analysis.
library("dplyr")
my_db <- src_postgres(dbname = "database-name",
host = "localhost",
port = 5432,
user = "username",
password = "password")
df <- tbl(my_db, "my_table")
df %>% filter(batch_name == "batch_A_1")
Using DBI and RPostgreSQL
Get the table by sending sql query
library("DBI")
library("RPostgreSQL")
m <- dbDriver("PostgreSQL")
con <- dbConnect(drv = m,
dbname = "database-name",
host = "localhost",
port = 5432,
user = "username",
password = "password")
df <- dbGetQuery(con, "SELECT * FROM my_table WHERE batch_name %LIKE% 'batch_A_%'")
library("dplyr")
df %>% filter(batch_name == "batch_A_1")