我想通過一個因子變量求和一組POSIXct對象,但得到的錯誤不是爲POSIXt對象定義sum
。然而,如果我只是計算平均值,它工作得很好。但是,我怎樣才能通過使用tapply的小組得到總結時間?R:使用tapply求和POSIXct對象
實施例:
data <- data.frame(time = c("2:50:04", "1:24:10", "3:10:43", "1:44:26", "2:10:19", "3:01:04"),
group = c("A","A","A","B","B","B"))
data$group <- as.factor(data$group)
data$time <- as.POSIXct(paste("1970-01-01", data$time), format="%Y-%m-%d %H:%M:%S", tz="GMT")
# works
tapply(data$time, data$group, mean)
# doesn't work
tapply(data$time, data$group, sum)
試試'tapply(data $ time,data $ group,function(x)sum(as.nume ric(x)))' –
太棒了,這是我所希望的一種簡單的解決方法。只需要轉換回h:m:s格式,這非常簡單。謝謝! – ageil