将序列中的值分配给一组连续的行，而使某些行为空 [英] Assigning values in a sequence to a group of consecutive rows leaving some rows empty

问题描述

我试图将几个连续的行分组（并为其分配相同的值），同时使某些行保持空白（当不满足特定条件时）。

I'm trying to group several consecutives rows (and assigning them the same value) while leaving some of the rows empty (when a certain condition is not fulfilled).

我的数据是位置（xy坐标），测量它们的日期/时间以及测量之间的时间跨度。以某种方式简化后，它们看起来像这样：

My data are locations (xy coordinates), the date/time at which they were measured, and the time span between measures. Somehow simplified, they look like this:

ID   X     Y      Time    Span
1    3445  7671   0:00    -
2    3312  7677   4:00    4
3    3309  7680   12:00   8
4    3299  7681   16:00   4
5    3243  7655   20:00   4
6    3222  7612   4:00    8
7    3260  7633   0:00    4
8    3254  7641   8:00    8
9    3230  7612   0:00    16
10   3203  7656   4:00    4
11   3202  7678   8:00    4
12   3159  7609   20:00   12
...

我想为在4个小时内测量的每个位置序列分配一个值，并使我的数据看起来像这样：

I'd like to assign a value to every sequence of locations that are measured within a time span of 4 hours, and make my data look like this:

ID   X     Y      Time    Span  Sequence
1    3445  7671   0:00    -     -
2    3312  7677   4:00    4     1
3    3309  7680   12:00   8     NA
4    3299  7681   16:00   4     2
5    3243  7655   20:00   4     2
6    3222  7612   4:00    8     NA
7    3260  7633   0:00    4     3
8    3254  7641   8:00    8     NA
9    3230  7612   0:00    16    NA
10   3203  7656   4:00    4     4
11   3202  7678   8:00    4     4
12   3159  7609   20:00   12    NA

我尝试了几次带有循环 for加上 ifelse条件的算法，例如：

I've tried several algorithms with a loop "for" plus "ifelse" condition like:

Sequence <- for (i in 1:max(ID)) {
ifelse (Span <= 4, i+1, "NA")
}

没有任何运气。我知道我的尝试是不正确的，但是我的编程技能确实很基础，而且我在网络上还没有发现任何类似的问题。

without any luck. I know my attempt is incorrect, but my programming skills are really basic and I haven't found any similar problem in the web.

任何想法都将不胜感激！

Any ideas would be very appreciated!

推荐答案

下面是一个很长的衬里：

Here is a longish one liner:

ifelse(x <- DF$Span == 4, cumsum(c(head(x, 1), tail(x, -1) - head(x, -1) == 1)), NA)
# [1] NA  1 NA  2  2 NA  3 NA NA  4  4 NA

说明：

• x 是TRUE / FALSE的向量，显示了 Span 是 4 。


• tail（x，- 1）是写 x [2：length（x）]


• <$的安全方法c $ c> head（x，-1）是写 x [1：（length（x）-1）] 的安全方法


• tail（x，-1）-head（x，-1）== 1 是TRUE / FALSE的向量，显示我们从 Span！= 4 到 Span == 4 的位置。


• 因为上面的向量比 x ，我在它前面加上 head（x，1）。 head（x，1）是写 x [1] 的安全方法。


• 然后我将 cumsum 转换为真/假向量，将其转换为整数递增的向量：其中 Span 从！= 4 跳到 == 4 ，它增加1，否则保持不变。


• 所有内容都包裹在 if $code>中，因此您只会看到 x 为TRUE的数字，即，其中 Span == 4 。



• x is a vector of TRUE/FALSE showing where Span is 4.
• tail(x, -1) is a safe way of writing x[2:length(x)]
• head(x, -1) is a safe way of writing x[1:(length(x)-1)]
• tail(x, -1) - head(x, -1) == 1 is a vector of TRUE/FALSE showing where we went from Span != 4 to Span == 4.
• since the vector above is one element shorter than x, I prepended head(x, 1) in front of it. head(x, 1) is a safe way of writing x[1].
• Then I take the cumsum so it converts the vector TRUE/FALSE into a vector of increasing integers: where Span jumps from !=4 to ==4 it increases by 1, otherwise stays constant.
• Everything is wrapped into an ifelse so you only see numbers where x is TRUE, i.e., where Span == 4.

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