R dplyr窗口函数，获取下一个满足某些条件的x窗口中的第一个值 [英] R dplyr window function, get the first value in the next x window that fulfil some condition

问题描述

我有一些dplyr数据框，并且有一些条件.我想知道每个单元格与下一个x行中符合条件的第一个单元格的索引是什么.

I have some dplyr dataframe and I have some condition. I want to know for each cell what is the index of the first cell that matches the condition in the next x rows.

在我的情况下，我希望有一个附加列，该列包含第一个值的索引，该索引至少比z中的当前值大.

In my case, I want to have an additional column that holds the index of the first value that was larger than the current value in at least z.

示例:在这里，我们正在寻找下3行中第一个值的索引，该索引比当前值大至少3倍.在第一行的情况下，该值为0，并且接下来的3个单元格中的至少大于3的第一个值为单元格编号4，其值为= 3.

Example: here we are looking for the index of the first value in the next 3 rows that is larger by at least 3 from the current value. In the case of the first row, the value is 0 and the first value in the next 3 cells that is larger by at least 3 is cell number 4 where its value = 3.

在第三行中，值= 2，在接下来的3行中，没有与条件匹配的值，因此我们得到的值为NA

In the third row, the value = 2 and in the next 3 rows there is no value that matches the condition so we get a value of NA

  value index_of_matched_cell
1     0                       4
2     0                       4
3     2                      NA
4     3                       7
5     3                       7
6     3                       7
7     6                      NA
8     6                      NA
9     6                      NA

谢谢！

推荐答案

这是使用 zoo 中的 rollapply 的一种方法:

Here is one way using rollapply from zoo :

next_rows <- 3
larger_than <- 3

with(df, zoo::rollapply(seq_along(value), next_rows + 1, function(x) 
               x[which(value[x] >= (value[x[1]] + larger_than))[1]],
               align = 'left', fill = NA))

#[1]  4  4 NA  7  7  7 NA NA NA

在 rollapply 中，我们迭代窗口大小为 next_rows + 1 的每一行的索引(因为我们要考虑接下来的3行和 rollapply 也会考虑当前行).我们将当前的 value 与接下来的3个值进行比较，并返回大于或等于 larger_than 值的第一个索引，并返回其索引.

In rollapply we iterate over the index of each row with window size of next_rows + 1 (since we want to consider next 3 rows and rollapply also considers current row). We compare the current value with next 3 values and return the first index where it is greater or equal to than larger_than value and return it's index.

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