当两个变量与第二个 DF 匹配时，将列添加到 DF

Question

我希望在 DF1 中添加另一列，在该列下方 returns 观察年份相关国家/地区的人口。即当国家和年份与 DF2 匹配时，人口被添加到 DF2 中的列。我之前用merge只匹配一个变量，有没有方法可以完成两个变量？

DF1:

eventid    |iyear | imonth| iday | CountryTxt
1.97000e+1 |1970  |      7|    2 |  Albania
1.97000e+11|  1970|      0|    0 |  United Kingdom
1.97001e+11|  1984|      1|    0 |  Somalia
1.97001e+11|  1990|      1|    0 |  France
1.97001e+11|  1991|      1|    0 |  New Zealand

DF2:

Country.Name|Code|Year|Population
Aruba       |ABW |1960| 123
Afganistan  |AFG |1970| 456
Albania     |ALB |1970| 1000
France      |FRA |1990| 5000

Answer 1

这完全在 merge() 的能力范围内：请注意 ?merge 引述中所有强调的词都是复数，即该函数可以在多个匹配列上工作...

by, by.x, by.y: specifications of the columns used for merging. See ‘Details’.
...
By default the data frames are merged on the columns with names they both have, but separate specifications of the columns can be given by ‘by.x’ and ‘by.y’. The rows in the two data frames that match on the specified columns are extracted

merge(df1,df2,
      by.x=c("iyear","CountryTxt"),
      by.y=c("Year","Country.Name"))

  iyear CountryTxt     eventid imonth iday Code Population
1  1970    Albania 1.97000e+01      7    2  ALB       1000
2  1990     France 1.97001e+11      1    0  FRA       5000

数据设置

df1 <- read.table(header=TRUE,sep="|",  strip.white=TRUE, text="
eventid    |iyear | imonth| iday | CountryTxt
1.97000e+1 |1970  |      7|    2 |  Albania
1.97000e+11|  1970|      0|    0 |  United Kingdom
1.97001e+11|  1984|      1|    0 |  Somalia
1.97001e+11|  1990|      1|    0 |  France
1.97001e+11|  1991|      1|    0 |  New Zealand
")

df2 <- read.table(header=TRUE,sep="|",  strip.white=TRUE, text="
Country.Name|Code|Year|Population
Aruba       |ABW |1960| 123
Afganistan  |AFG |1970| 456
Albania     |ALB |1970| 1000
France      |FRA |1990| 5000
")

当两个变量与第二个 DF 匹配时，将列添加到 DF

add column to DF when two variables are matched with second DF

lookup

merge

r

dataframe

数据设置