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r - 如何从 read.csv 生成的数据框而不是列表中获取单个值？

问题描述

我在数据路径上使用 read.csv。它返回一个数据框。我希望能够在此数据框中获取单个值，但我得到了显示级别的值列表。

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了什么以及得到的结果。

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])

我想要的是访问一个值：例如，“番茄”或“硝酸盐”。我想要的结果正是这样：

>[1] tomato

这是我尝试过的和得到的结果：

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。如果您希望我将帖子编辑得更清楚，请告诉我。谢谢你。

标签： rcsvdataframeread.csv

解决方案

一些建议

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

输入数据后，您可以按如下方式对其进行操作

# 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"

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