如何从 read.csv 生成的数据帧而不是列表中获取单个值？

Question

我在数据路径上使用 read.csv。 它返回一个数据帧。 我希望能够在此数据框中获得单个值，但我获得了一个显示级别的值列表。

我尝试了几种方法来访问我想要的值。 在下一部分中，我将向您展示我尝试过的方法以及得到的结果。

这是我的简单数据框：

"OGM","Nutrient","data3"
"tomato","iron",0.03
"domestic cat","iron",0.02
"zebrafish","zing",0.02
"giraffe","nitrate", 0.09
"common cougar","manganese",0.05
"fawn","nitrogen",0.04
"daim","bromure",0.08
"wild cat","iron",0.05
"domestic cat","calcium",0.02
"muren","calcium",0.07
"jaguar","iron",0.02
"green turtle","sodium",0.01
"dave grohl","metal",0.09
"zebra","nitrates",0.12
"tortoise","sodium",0.16
"dinosaur","calcium",0.08
"apex mellifera","sodium",0.15

这是我加载数据的方式：

   #use read.csv on the datapath contained in file   
   fileData <- read.csv(file[4][[1]])
   print(fileData[1][1])

---

我想要的是访问单个值：例如“番茄”或“硝酸盐”。 我想要的结果正是这样：

>[1] tomato

---

这是我的尝试和结果：

print(fileData[1][1])返回

>  OGM
>1          tomato
>2    domestic cat
>3       zebrafish
>4         giraffe...

print(fileData$OGM[1])返回

>  [1] tomato
Levels: apex mellifera common cougar daim...

print(fileData[1][[1]])返回

> [1] tomato         domestic cat   zebrafish      giraffe        common cougar [...]       
[15] tortoise       dinosaur       apex mellifera
Levels: apex mellifera common cougar daim...

print(fileData$OGM[[1]])返回

Levels: apex mellifera common cougar daim...

为这个愚蠢的问题道歉，但我有点迷茫。 感谢所有帮助。 如果你想让我编辑我的帖子更清楚，告诉我。 谢谢你。

Answer 1

一些建议

尝试readr::read_csv而不是read.csv来读入您的数据。 这将解决stringsAsFactors 问题。 或者使用 Stewart Macdonald 建议的方法。

输入数据后，您可以按如下方式操作它

# Make a sample dataframe

library(tidyverse)


df <- tribble(~OGM, ~Nutrient, ~data3,
"tomato","iron",0.03,
"domestic cat","iron",0.02,
"zebrafish","zing",0.02,
"giraffe","nitrate", 0.09,
"common cougar","manganese",0.05,
"fawn","nitrogen",0.04,
"daim","bromure",0.08,
"wild cat","iron",0.05,
"domestic cat","calcium",0.02,
"muren","calcium",0.07,
"jaguar","iron",0.02,
"green turtle","sodium",0.01,
"dave grohl","metal",0.09,
"zebra","nitrates",0.12,
"tortoise","sodium",0.16,
"dinosaur","calcium",0.08,
"apex mellifera","sodium",0.15)

df %>% 
  select(OGM) %>% # select the OGM column
  filter(OGM == 'tomato') %>% 
  pull # convert to a vector

[1] "tomato"