ifelse&使用dplyr进行SQL in-db操作时的grepl命令 [英] ifelse & grepl commands when using dplyr for SQL in-db operations
问题描述
在运行在R数据框上的dplyr中，很容易运行
In dplyr running on R data frames, it is easy to run
df <- df %>%
mutate(income_topcoded = ifelse(income > topcode, income, topcode)
现在使用大型SQL数据库，使用dplyr将命令发送到SQL服务器当我运行相同的命令时，我回到
I'm now working with a large SQL database, using dplyr to send commands to the SQL server. When I run the same command, I get back
Error in postgresqlExecStatement(conn, statement, ...) :
RS-DBI driver: (could not Retrieve the result : ERROR:
function ifelse (boolean, numeric, numeric) does not exist
HINT: No function matches the given name and argument types. You may need to add explicit type casts.
你如何建议实现 ifelse（）语句？我会在PivotalR（似乎支持 ifelse（），但是我不知道如何将它与dplyr进行集成，无法在SO上找到任何示例），我可以使用的一些SQL语法在这里，或者我不知道的dplyr的某些功能。
How would you suggest implementing ifelse() statements? I'd be fine with something in PivotalR (which seems to support ifelse(), but I don't know how to integrate it with dplyr and couldn't find any examples on SO), some piece of SQL syntax which I can use in-line here, or some feature of dplyr which I was unaware of.
（我有同样的问题，我想使用 grepl（） 作为一个in-db操作，但我不知道该怎么做。）
(I have the same problem that I'd like to use grepl() as an in-db operation, but I don't know how to do so.)
推荐答案
根据@ hadley对此线程的回复，您可以使用SQL风格的<在dplyr的数据库数据框中，code> if（）语句 mutate（）
Based on @hadley's reply on this thread, you can use an SQL-style if() statement inside mutate() on dplyr's in-db dataframes:
df <- df %>%
mutate( income_topcoded = if (income > topcode) income else topcode)
只要使用 grepl（）去...好吧，你不行。但是您可以使用SQL ，如 operator：
As far as using grepl() goes...well, you can't. But you can use the SQL like operator:
df <- df %>%
filter( topcode %like% "ABC%" )
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