r_code

Import data by Base functions

参考 Schouwenaars (2016)

stringsAsFactors = FALSE

Import strings as categorical variables?

txt 文件读取

# Import hotdogs.txt: hotdogs
hotdogs <- read.delim("datasets/hotdogs.txt",sep = '\t',header = F)

# Summarize hotdogs
summary(hotdogs)

##        V1           V2              V3       
##  Beef   :20   Min.   : 86.0   Min.   :144.0  
##  Meat   :17   1st Qu.:132.0   1st Qu.:362.5  
##  Poultry:17   Median :145.0   Median :405.0  
##               Mean   :145.4   Mean   :424.8  
##               3rd Qu.:172.8   3rd Qu.:503.5  
##               Max.   :195.0   Max.   :645.0

注意 sep = '\t'

library(xfun)

## 
## Attaching package: 'xfun'

## The following objects are masked from 'package:base':
## 
##     attr, isFALSE

library(magrittr)
read_utf8("datasets/hotdogs.txt") %>% head

## [1] "Beef\t186\t495" "Beef\t181\t477" "Beef\t176\t425" "Beef\t149\t322"
## [5] "Beef\t184\t482" "Beef\t190\t587"

\t 就是分割符号。

指定变量名称

可以指定对应的 column name

# Finish the read.delim() call
hotdogs <- read.delim("datasets/hotdogs.txt", header = F, col.names = c("type", "calories", 'sodium'))

# Select the hot dog with the least calories: lily
lily <- hotdogs[which.min(hotdogs$calories), ]

# Select the observation with the most sodium: tom
tom <- hotdogs[which.max(hotdogs$sodium), ]

# Print lily and tom
lily

##       type calories sodium
## 50 Poultry       86    358

tom

##    type calories sodium
## 15 Beef      190    645

which.max和which.min，反馈 index，类似于 (\arg\max_{\text{index}}\text{variable})。

Schouwenaars, Filip. 2016. “Importing Data in R (Part 1).” 2016. <https://www.datacamp.com/courses/importing-data-in-r-part-1>.