R：提取列中的部分字符串

Question

你好 stackoverflow 社區，

我在數據集中有以下問題。 我必須提取“BMI”列中字符串的前四個符號，然后將它們轉換為數字。

例如：而不是“23.3 [21.9-24.6]”-> 23.3

你可以在這里找到數據： https://github.com/tanaytuncer/LifeExpectancy_BMI

library(mosaic)
library(tidyverse)

path <- "/Users/tanaytuncer/Desktop/Quantitative Datenanalyse/BMI.csv"
df_BMI <- read.csv(path)
df_BMI <- df_BMI[-1:-3, ]
df_BMI <- df_BMI %>%
  rename(country = "X",
         "2000" = "X2000",
         "2001" = "X2001",
         "2002" = "X2002",
         "2003" = "X2003",
         "2004" = "X2004",
         "2005" = "X2005",
         "2006" = "X2006",
         "2007" = "X2007",
         "2008" = "X2008",
         "2009" = "X2009",
         "2010" = "X2010",
         "2011" = "X2011",
         "2012" = "X2012",
         "2013" = "X2013",
         "2014" = "X2014",
         "2015" = "X2015"
         )
df_BMI <- df_BMI %>%
  gather("year", "BMI", 2:17)

Answer 1

我們可以使用substr

df_BMI$BMI <- as.numeric(substr(df_BMI$BMI, 1, 4))

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或者使用來自parse_number的readr

library(readr)
df_BMI$BMI <- parse_number(df_BMI$BMI)

---

在不gather成“長”格式的情況下，我們也可以使用across

library(dplyr)
df_BMI1 <-  df_BMI %>%
       mutate(across(-country, parse_number))

---

如果我們使用check.names = FALSE可以避免rename

df_BMI <- read.csv("https://raw.githubusercontent.com/tanaytuncer/LifeExpectancy_BMI/main/BMI.csv", check.names = FALSE)
df_BMI <- df_BMI[-1:-3, ]
names(df_BMI)[1] <- "country"