我有两个数据框:
purchases:
time quantity
1: 2013-07-31 03:42:02 30
2: 2013-07-31 03:59:32 30
3: 2013-07-31 04:02:22 28
....
history:
time price
1: 2013-07-31 04:26:46 10
2: 2013-07-31 07:11:01 10
3: 2013-07-31 08:16:36 5
4: 2013-07-31 08:40:03 8
5: 2013-07-31 08:47:56 7
....
我想做的事:
对于“购买”中的每一行,在“历史记录”中查找日期最接近的行(如果可能小于“购买”中的行)
我试图做这样的事情
history <- as.vector(history$time)
对于购买中的每一行:
current.price <- purchases[i,]$time
which(history-current.price)==min(history-current.price)
如果值是数字,这很有用,但我不知道如何处理 POSIXct 类的这些日期。
EDIT:添加了可重现的数据
#Reproducible dummy data
p <- read.table(text="
t,quantity
2013-07-31 03:42:02,30
2013-07-31 03:59:32,30
2013-07-31 04:02:22,28",header=TRUE,sep=",")
h <- read.table(text="
t,price
2013-07-31 04:26:46,10
2013-07-31 07:11:01,10
2013-07-31 08:16:36,5
2013-07-31 08:40:03,8
2013-07-31 08:47:56,7",header=TRUE,sep=",")
#Convert to POSIXct
p$t <- as.POSIXct(strptime(p$t, "%Y-%m-%d %H:%M:%S"))
h$t <- as.POSIXct(strptime(h$t, "%Y-%m-%d %H:%M:%S"))