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r - 仅选择具有特定时差的相关行

问题描述

这是我的数据：


    > str(heard2)
'data.frame':   616 obs. of  3 variables:
 $ DateTime   : POSIXct, format: "2017-07-26 22:28:10" "2017-07-26 22:31:18" "2017-07-26 22:32:18" ...
 $ Transmitter: int  30759 30759 30759 30759 30759 30759 30759 30759 30759 30759 ...
 $ Station    : Factor w/ 35 levels "TRA1-69","TRA2-69",..: 21 21 21 21 21 22 21 22 21 22 ...

> dput(heard2[c(37:47),])
structure(list(DateTime = structure(c(1501109904, 1501109950, 
1501109953, 1501110005, 1501110008, 1501110053, 1501110056, 1501110105, 
1501110108, 1501110166, 1501110169), class = c("POSIXct", "POSIXt"
), tzone = "GMT"), Transmitter = c(30759L, 30759L, 30759L, 30759L, 
30759L, 30759L, 30759L, 30759L, 30759L, 30759L, 30759L), Station = structure(c(21L, 
22L, 21L, 22L, 21L, 22L, 21L, 22L, 21L, 22L, 21L), .Label = c("TRA1-69", 
"TRA2-69", "TRA3-69", "TRA4-69", "TRA5-69", "TRA6-69", "TRA7-69", 
"TRA8-69", "TRB1-69", "TRB2-69", "TRB3-69", "TRB4-69", "TRB5-69", 
"TRB6-69", "TRC1-69", "TRC2-69", "TRC3-69", "TRC4-69", "TRC5-69", 
"TRC6-69", "TRD1-69", "TRD2-69", "TRE1-69", "TRE2-69", "TRE3-69", 
"TRE4-69", "TRE5-69", "TRF1-69", "TRF2-69", "TRF3-69", "TRF4-69", 
"TRG1-69", "TRG2-69", "TRG3-69", "TRG4-69"), class = "factor")), row.names = 45:55, class = "data.frame")

日期时间列是指在特定站点检测到发射器的时间。大多数这些检测相隔 30-60 秒或更长时间。如何选择与仅相隔 8 秒（或更短）的时间对应的行？

标签： rdatetime

解决方案

编辑：如果您想要较早、较晚或两者的记录，原始请求尚不清楚。这会产生两个记录。

创建一个用于向前检查的变量 ( lead)，然后创建一个用于向后检查的变量 ( lag)。然后用于filter确定您是否想要第一个 (set dist_lead == 8)、后一个 (set dist_lag == 8) 或两者 (set filter(dist_lead == 8 | dist_lag == 8))。

k %>% 
mutate(dist_lead = ifelse(lead(Transmitter) == Transmitter,difftime(lead(DateTime), 
                         DateTime, units = "secs"), NA),
dist_lag = ifelse(lag(Transmitter) == Transmitter, difftime(DateTime, lag(DateTime), 
units = "secs"), NA)) %>% 
filter(dist_lead == 8)

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