將因子轉換爲POSIXlt並在R中有傳播日期

Question

我有一個帶有時間信息的矢量，每天只記錄一次日期。我需要將矢量轉換爲可用格式，例如POSIXlt。時間是有序的，一天中的所有時間（%H:%M）都屬於在無日期時間之前記錄的最後日期。

t <- structure(c(6L, 1L, 2L, 3L, 4L, 5L, 10L, 7L, 8L, 9L), 
    .Label = c("00:15", "00:25", "00:35", "00:45", "02:05", "20.01.2013; 0:05", 
    "20:48", "20:58", "21:08", "25.01.2013; 20:38"), class = "factor") 

從多個先前回答有關性因素問題至今轉換（例如here），我知道如何t[c(1, 7)]轉換。

t1 <- strptime(as.character(t[c(1, 7)]), format = "%d.%m.%Y; %H:%M") 
# t1 
# [1] "2013-01-20 00:05:00 CET" "2013-01-25 20:38:00 CET" 

但是，如何傳播剩餘值的缺失日期，以便他們將正確轉換？

Answer 1

library(zoo) # For the na.locf function 

df = data.frame(date=t) 

# Put date and time in separate columns 
df$time = gsub(".*; (.*)","\\1", df$date) 
df$date = as.Date(df$date, format="%d.%m.%Y") 

# Fill missing df$date values 
df$date = na.locf(df$date) 

# Convert to POSIXct 
df$date = as.POSIXct(paste(df$date, df$time)) 
df = df[,1, drop=FALSE] 

df 

        date 
1 2013-01-20 00:05:00 
2 2013-01-20 00:15:00 
3 2013-01-20 00:25:00 
4 2013-01-20 00:35:00 
5 2013-01-20 00:45:00 
6 2013-01-20 02:05:00 
7 2013-01-25 20:38:00 
8 2013-01-25 20:48:00 
9 2013-01-25 20:58:00 
10 2013-01-25 21:08:00 

Answer 2

我們可以使用dplyr

library(dplyr) 
data.frame(t) %>% 
    mutate(Date = as.Date(t, "%d.%m.%Y")) %>% 
    group_by(grp = cumsum(!is.na(Date))) %>% 
    mutate(Date = Date[1L], 
      DateTime = as.POSIXct(paste(Date, sub(".*;", "", t)))) %>% 
    ungroup() %>% 
    select(DateTime) 
#   DateTime 
#    <dttm> 
#1 2013-01-20 00:05:00 
#2 2013-01-20 00:15:00 
#3 2013-01-20 00:25:00 
#4 2013-01-20 00:35:00 
#5 2013-01-20 00:45:00 
#6 2013-01-20 02:05:00 
#7 2013-01-25 20:38:00 
#8 2013-01-25 20:48:00 
#9 2013-01-25 20:58:00 
#10 2013-01-25 21:08:00 

---

或者使用base R

i1 <- nchar(as.character(t))==5 
v1 <- ifelse(i1, paste(sub(";.*", ";", t[!i1])[cumsum(!i1)], 
        sub(".*;\\s+", "", t[i1])), as.character(t)) 

strptime(v1, "%d.%m.%Y %H:%M")