R减去相同ID的值(从显示的第一个ID中减去) [英] R subtract value for the same ID (from the first ID that shows)
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问题描述
我有一个与这里发现的问题类似的问题:
R,从上一行中减去值,然后按分组(稍作修改;请参见下文):
I have a similar question to the question found here: R, subtract value from previous row, group by (slight modification; see below):
在R中,可以说我有此数据。 / p>
In R, lets say I have this data.
Data
id date value
2380 10/30/12 21.01
2380 10/31/12 22.04
2380 11/1/12 22.65
2380 11/2/12 23.11
20100 10/30/12 35.21
20100 10/31/12 37.07
20100 11/1/12 38.17
20100 11/2/12 38.97
20103 10/30/12 57.98
20103 10/31/12 60.83
我想从相同ID的ID值中减去该值。我希望这是有道理的。见下文:)
And I want to subtract the value from the value of the ID of the same ID. I hope this makes sense. See below :)
id date value diff
2380 10/30/12 21.01 0
2380 10/31/12 22.04 1.03
2380 11/1/12 22.65 1.64
2380 11/2/12 23.11 2.10
20100 10/30/12 35.21 0
20100 10/31/12 37.07 1.86
20100 11/1/12 38.17 2.96
20100 11/2/12 38.97 3.76
20103 10/30/12 57.98 0
20103 10/31/12 60.83 2.85
感谢您的帮助!
推荐答案
假设日期已经排序。我可能会检索每个id的第一个值,然后使用它来计算diff功能。
这样的事情。
Let's assume that dates are already sorted. I would probably retrieve the first value for each id and then use this to compute the diff feature. Something like this.
my.df <- data.frame(
id = c(2380, 2380, 2380, 2380, 20100,20100,20100, 20100, 20103, 20103),
date = c("10/30/12", "10/31/12", "11/1/12", "11/2/12", "10/30/12", "10/31/12", "11/1/12", "11/2/12", "10/30/12", "10/31/12"),
value = c(21.01, 22.04, 22.65, 23.11, 35.21, 37.07, 38.17, 38.97, 57.98, 60.83),
stringsAsFactors = F)
#
# get ids
my.ids <- unique(my.df$id) # or levels(my.df$id)
# get first val (assuming sorting by date)
id.val0 <- sapply(my.ids, (function(id){
my.df$value[my.df$id == id][1]
}))
names(id.val0) <- my.ids
# do operation
my.df$diff <- sapply(1:nrow(my.df), (function(i){
tmp.id <- my.df$id[i]
my.df$value[i] - id.val0[as.character(tmp.id)]
}))
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