想想R在這裏試圖做什麼。數據幀有8
行,但您要追加的向量只有6
元素。這些元素應該對齊到哪些行? R應該在另外兩個地方放些什麼?
library(zoo)
dataframe <- read.table(text="Date Value
21/07/2016 14.8
22/07/2016 14.9
23/07/2016 15.8
24/07/2016 15.0
25/07/2016 15.7
26/07/2016 15.6
27/07/2016 16.1
28/07/2016 16.1", header=TRUE)
rollmedian(dataframe$Value,k=3)
# [1] 14.9 15.0 15.7 15.6 15.7 16.1
nrow(dataframe) # [1] 8
length(rollmedian(dataframe$Value,k=3)) # [1] 6
因爲我能猜到你的意思(糾正我,如果我錯了),我會嘗試:
dataframe$medianval <- c(NA, NA, rollmedian(dataframe$Value,k=3))
dataframe
# Date Value medianval
# 1 21/07/2016 14.8 NA
# 2 22/07/2016 14.9 NA
# 3 23/07/2016 15.8 14.9
# 4 24/07/2016 15.0 15.0
# 5 25/07/2016 15.7 15.7
# 6 26/07/2016 15.6 15.6
# 7 27/07/2016 16.1 15.7
# 8 28/07/2016 16.1 16.1
如果您希望能夠方便地適應這一點,你應該寫一簡單功能:
med.fun <- function(var, data, k){
# Note: variable name must be in quotes
return(c(rep(NA, k-1), with(data, rollmedian(get(var), k=k))))
}
med.fun("Value", dataframe, 5)
# [1] NA NA NA NA 15.0 15.6 15.7 15.7
非常感謝您的幫助和澄清。會以不同於c的方式存在(NA,NA,...例如,如果我想運行測試不同中值長度的循環, – carlosmaria