R语言代码优化：高效提取数据并计算百分比变化

above.select <- function(tmp.csv) { tmp.gp <- read.csv(paste0('testtd/', tmp.csv)) if (any(abs(tail(tmp.gp$td, 4)) > 0.3)) { tmp.zx <- tmp.gp %>% tail(20) %>% filter(abs(td) > 0.3) %>% select(meanzx) if (nrow(tmp.zx) >= 1) { tmp.above <- (tail(tmp.zx$meanzx, 1) - mean(tmp.zx$meanzx)) * 100 / mean(tmp.zx$meanzx) tmp.code <- substr(tmp.csv, start = 13, stop = 18) return(data.frame(code = tmp.code, above = tmp.above)) } } return(NULL) }