R/subset.td.data.frame.R

In nonsleepr/teradataR: Teradata R Package

subset.td.data.frame <- function(x, subset, select, drop = FALSE, ...) {
    if (!missing(subset)) {
        e <- substitute(subset)
        wc <- deparse(e)
        # r <- eval(e, x, parent.frame()) if (!is.logical(r)) stop(''subset' must evaluate to logical') r <- r & !is.na(r)
    }
    if (missing(select)) 
        vars <- TRUE else {
        nl <- as.list(seq_along(x))
        names(nl) <- names(x)
        vars <- eval(substitute(select), nl, parent.frame())
    }
    
    if (exists("wc")) {
        y <- x[vars]
        wc <- gsub("==", "=", wc)
        wc <- gsub("&&", " AND ", wc)
        wc <- gsub("&", " AND ", wc)
        wc <- gsub("||", " OR ", wc, fixed = TRUE)
        wc <- gsub("|", " OR ", wc, fixed = TRUE)
        wc <- gsub("^", "**", wc, fixed = TRUE)
        wc <- gsub("%%", " MOD ", wc)
        wc <- gsub("\"", "'", wc, fixed = TRUE)
        wc <- gsub("%in%", " IN ", wc)
        wc <- gsub("c(", "(", wc, fixed = TRUE)
        
        if (!is.null(attr(y, "whereClause"))) 
            wc <- paste(attr(y, "whereClause"), "AND", wc)
        
        attr(y, "whereClause") <- wc
        
        obj <- .td.object(attr(x, "tableName"), attr(x, "database"))
        query <- sprintf("SELECT CAST(COUNT(*) AS FLOAT) FROM %s WHERE %s", obj, wc)
        res <- try(tdQuery(query))
        if (!is.data.frame(res)) {
            warning("Invalid subset expression.")
            return(x[vars])
        }
        attr(y, "totalRows") <- as.numeric(res)
        return(y)
    }
    
    return(x[vars])
}