如何從 read.csv 生成的數據幀而不是列表中獲取單個值？

Question

我在數據路徑上使用 read.csv。 它返回一個數據幀。 我希望能夠在此數據框中獲得單個值，但我獲得了一個顯示級別的值列表。

我嘗試了幾種方法來訪問我想要的值。 在下一部分中，我將向您展示我嘗試過的方法以及得到的結果。

這是我的簡單數據框：

"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

這是我加載數據的方式：

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

---

我想要的是訪問單個值：例如“番茄”或“硝酸鹽”。 我想要的結果正是這樣：

>[1] tomato

---

這是我的嘗試和結果：

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...

為這個愚蠢的問題道歉，但我有點迷茫。 感謝所有幫助。 如果你想讓我編輯我的帖子更清楚，告訴我。 謝謝你。

Answer 1

一些建議

嘗試readr::read_csv而不是read.csv來讀入您的數據。 這將解決stringsAsFactors 問題。 或者使用 Stewart Macdonald 建議的方法。

輸入數據后，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"