Question

我已经创建了一个函数，它从文件列表中读取输入并使用rbind附加它。

dat <- NA
file.names <- list.files(paste(in.path2,"CSV",sep =""))
for(f in file.names){
  file <- paste(in.path2,"CSV/", f, sep = "")
  tmp <- read.csv(file, stringsAsFactors = F, na.strings = c("", " "))

  if (is.na(dat)) {
    dat <- tmp
  } else {
    colnames(tmp) <- colnames(dat)
    dat <- rbind(dat, tmp)
  }
  print(f)
}

我收到了这个警告：

 1: In if (is.na(dat)) { ... :
  the condition has length > 1 and only the first element will be used.

如何纠正？

Answer 1

我强烈建议不要像这样增长你的数据框架

file.names <- list.files(paste(in.path2,"CSV",sep =""))
input_list <- list()
for(f in file.names){
  file <- paste(in.path2,"CSV/", f, sep = "")
  input_list[[f]] <- read.csv(file, stringsAsFactors = F, na.strings = c("", " "))
  print(f)
}
dat <- do.call(rbind, input_list)

这要快得多，你不需要测试dat is.na或不是

Answer 2

我们可以使用lapply更轻松地执行此操作，而无需担心NA和if/else条款的分配

filenames <- list.files(paste0(in.path2,"CSV"), full.names = TRUE)
do.call(rbind,lapply(filenames, read.csv, na.strings = c("", " "), stringsAsFactors = FALSE))

或其他选项fread来自data.table

library(data.table)
rbindlist(lapply(filenames, fread, na.strings = c("", " ")), fill = TRUE)

或tidyverse

library(tidyverse)
map_df(filenames, read_csv, na = c("", " "))

如果列不相同，则

map(filenames, read_csv, na = c("", " ")) %>%
      bind_rows

如何更正此警告“条件有长度＆gt;来自`if`功能的警告1＆＃34;？

2 个答案: