R 创建数据框dataframe示例

id = c(1,2,1,4,2)
year = c(1980, 1990, 2000, 2010, 2020)
salary = c(2000, 3000, 4000, 5000, 6000)
df = data.frame(id, year, salary);
df

# id year salary
# 1  1 1980   2000
# 2  2 1990   3000
# 3  1 2000   4000
# 4  4 2010   5000
# 5  2 2020   6000