[英]hHw to pass a system function to MonetDB through R?
使用MonetDB.R
,我想运行此命令,但是我不想打开mclient。 有通用的方法可以做到这一点吗?
create function div_noerror(l double, r double) returns double
来自MonetDB.R
的作者MonetDB.R
您可以在数据库中创建它。 如果它已经存在,它将失败,但是您可以捕获该错误。 所以
dbSendQuery(con, "create function div_noerror(l double, r double) returns double external name calc.div_noerror”) should work.
这是一个稍长的用法示例:
# example of division
dbGetQuery( con , "SELECT 1 / 2 AS a" )
# example of division by zero, which causes an error
dbGetQuery( con , "SELECT 1 / 0 AS a" )
# load the `div_noerror` function through a system call
dbSendQuery( con , "CREATE FUNCTION div_noerror(l DOUBLE, r DOUBLE) RETURNS DOUBLE EXTERNAL NAME calc.div_noerror" )
# use the div_noerror function instead of the `/` operator
dbGetQuery( con , "SELECT div_noerror( 1 , 2 ) AS a" )
# division by zero now returns a missing instead of crashing the entire query
dbGetQuery( con , "SELECT div_noerror( 1 , 0 ) AS a" )
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