Question

从SO（Join data.table on exact date or if not the case on the nearest less than date）的其他地方窃取一个虚拟示例，我希望根据第一个日期（Dt1中的日期）严格早于第二个日期（Dt2中的日期）加入两个表。

还关闭了DataCombine解决方案的'slide'功能中的'warning'消息，因为它可能会不公平地减慢mtotos解决方案的速度。

library(data.table)

Dt1 <- read.table(text="
date      x
1/26/2010,  10  
1/25/2010,  9  
1/24/2010,  9   
1/22/2010,  7    
1/19/2010,  11", header=TRUE, stringsAsFactors=FALSE)

Dt2 <- read.table(text="
date
1/26/2010   
1/23/2010   
1/20/2010", header=TRUE, stringsAsFactors=FALSE)

加入所需的结果

   date     x  
1/26/2010 - 9 # based on closest observation strictly less than date  
1/23/2010 - 7   
1/20/2010 - 11

两种解决方案的时间

（我保留data.frame格式以输入mtoto的解决方案，并保留jangorecki的data.table）。

solution.mtoto = function(Df1, Df2)
{
  #Full outer join of two df's
  merged <- merge(Df1, Df2, by = "date", all = T, sort=T)

  # Shifting values backwards by one using 'slide' from DataCombine
  merged <- slide(merged, Var = "x", slideBy = -1, reminder = F)

  # Inner join retaining the relevant cols
  return(merge(Df2,merged)[,-2])
}

solution.jangorecki = function(Dt1, Dt2)
{
  offset.roll.join = function(Dt1, Dt2){
    Dt2[, jndate := date - 1L] # produce join column with offset
    on.exit(Dt2[, jndate := NULL]) # cleanup join col on exit
    Dt1[Dt2, .(date = i.date, x), on = c("date" = "jndate"), roll = Inf] # do rolling join
  }
  return(offset.roll.join(Dt1, Dt2))
}

res.mtoto = sapply(1:10, FUN = function(x){system.time({solution.mtoto(Df1, Df2)})})

res.jangorecki = sapply(1:10, FUN = function(x){system.time({solution.jangorecki(Dt1, Dt2)})})


> res.mtoto[c("user.self", "sys.self"),]
           [,1]  [,2]  [,3]  [,4]  [,5]  [,6]  [,7]  [,8]  [,9] [,10]
user.self 0.004 0.004 0.004 0.004 0.003 0.003 0.003 0.003 0.003 0.003
sys.self  0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

> res.jangorecki[c("user.self", "sys.self"),]
           [,1]  [,2]  [,3]  [,4]  [,5]  [,6]  [,7]  [,8]  [,9] [,10]
user.self 0.005 0.005 0.004 0.004 0.005 0.004 0.004 0.004 0.003 0.004
sys.self  0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

编辑，在mtoto的解决方案中意外地引用了Dt1而不是Df1。现在修复了。

类似的速度（在更大的数据集上可能更明显？）。我的另一个问题是我希望第二个表格中返回的日期。

例如，期望的结果是：

date - x - date2
1/26/2010 - 9 - 1/25/2010
1/23/2010 - 7 - 1/22/2010
1/20/2010 - 11 - 1/19/2010

Answer 1

使用-1L偏移滚动连接。

更新2016-04-02 ：在当前开发版中使用this commit v1.9.7，可以在不创建临时列的情况下完成此操作。来自NEWS：

x的列可以始终使用前缀j在x.中引用。当x的列也是连接列时，这尤其有用。这是一个解决#1615的补丁。

Dt2[, jndate := date - 1L]
Dt1[Dt2,
    .(date = i.date, orgdate = x.date, x),
    on = c("date" = "jndate"),
    roll = Inf]
#         date    orgdate  x
#1: 2010-01-26 2010-01-25  9
#2: 2010-01-23 2010-01-22  7
#3: 2010-01-20 2010-01-19 11

原始答案，如果您的年龄为1.9.6或更高，则非常有用。

library(data.table)

# data
Dt1 = fread("date      x
1/26/2010,  10  
1/25/2010,  9  
1/24/2010,  9   
1/22/2010,  7    
1/19/2010,  11")[, date := as.IDate(date, format=("%m/%d/%Y"))][]
Dt2 = fread("date
1/26/2010   
1/23/2010   
1/20/2010")[, date := as.IDate(date, format=("%m/%d/%Y"))][]

# solution
offset.roll.join = function(Dt1, Dt2){
    Dt2[, jndate := date - 1L] # produce join column with offset
    Dt1[, orgdate := date] # should not be needed after data.table#1615
    on.exit({Dt2[, jndate := NULL]; Dt1[, orgdate := NULL]}) # cleanup on exit
    Dt1[Dt2, .(date = i.date, orgdate, x), on = c("date" = "jndate"), roll = Inf] # do rolling join
}
offset.roll.join(Dt1, Dt2)
#         date    orgdate  x
#1: 2010-01-26 2010-01-25  9
#2: 2010-01-23 2010-01-22  7
#3: 2010-01-20 2010-01-19 11

Answer 2

分三步：

library(DataCombine)

#Full outer join of two df's
merged <- merge(Dt1, Dt2, by = "date", all = T)

# Shifting values backwards by one using 'slide' from DataCombine
merged <- slide(merged, Var = "x", slideBy = -1)

# Inner join retaining the relevant cols
merge(Dt2,merged)[,-2]
#       date x-1
#1 1/20/2010  11
#2 1/23/2010   7
#3 1/26/2010   9

在日期加入两个data.tables，表1中最接近的日期严格小于第二个表

两种解决方案的时间

2 个答案: