Question

I was wondering if anybody could help...

I have a data frame which includes a continuous time column and I am trying to remove all rows below a specified time.

The data starts from approx. 11:29:00 but I want to remove all rows before the time 12:30.00 and after the time 14:20.00. Since the data is recorded every second, deleting unnecessary rows will be a great help and make managing this data a whole lot easier for me so any help would be greatly appreciated.

This is the head of the data frame, as you can see the time is continuous in seconds. I would like to remove all these rows up to 12:30:00 within the GPS.Time column. Hope that makes sense.

        Raw.Vel.        Smooth.Vel.        GPS.Time

        1.486               0.755         11:39:39
        1.425               1.167         11:39:40
        1.466               1.398         11:39:41
        1.533               1.552         11:39:42
        1.517               1.594         11:39:43
        1.918               1.556         11:39:44

Creating above data frame:

Raw.Vel. <- c(1.486,1.425, 1.466, 1.533, 1.517, 1.918)
Smooth.Vel. <- c(0.755, 1.167, 1.398, 1.552, 1.594, 1.556)
GPS.Time <- c("11:39:39", "11:39:40", "11:39:41", "11:39:42", "11:39:43", "11:39:44")
sample <- data.frame(Raw.Vel., Smooth.Vel., GPS.Time)

Thanks in advance.

Answer 1

将GPS.Time转换为＆＃34; POSIXct＆＃34;对象：

df$time <- as.POSIXct(df$GPS.Time, format="%H:%M:%S")

然后你可以使用逻辑过滤：

filtered_df <- df[df$time < as.POSIXct("12:30:00", format="%H:%M:%S"), ]

Answer 2

使用lubridate包将您的字符串时间列转换为某种时间类：

library(lubridate) 
sample$GPS.Time <- hms(sample$GPS.Time)

要获得所需的输出，只需使用带括号（[）的子集，并满足您想要的条件。在您的示例中，我删除了所有行，直到11:39:42。

output <- sample[sample$GPS.Time < hms("11:39:42"),]

Answer 3

您可以转换＆＃34; GPS.Time＆＃34;中的条目。列成字符（这最初是一个因子变量）。之后，您可以通过将时间与指定的截止时间进行比较来分离集合，该截止时间存储为应以相同格式（HH：MM：SS）写入的字符串：

sample$GPS.Time <- as.character(sample$GPS.Time)
cutoff_time <- "11:39:42" # modify as necessary
sample <- sample[-which(sample$GPS.Time < cutoff_time),] #remove all rows with times smaller than the cutoff_time
#> sample
#    Raw.Vel. Smooth.Vel. GPS.Time
#4    1.533       1.552 11:39:42
#5    1.517       1.594 11:39:43
#6    1.918       1.556 11:39:44

Removing rows of data in R below a specified value

3 个答案: