[英]How to calculate moving average from previous rows in data.table?
我有這樣的數據;
library(data.table)
set.seed(1)
df <- data.table(store = sample(LETTERS[1:2],size = 10,replace = T),
week = sample(1:10),
demand = round(sample(rnorm(10,mean = 20,sd=2)),2))
random_na_index <- sample(1:nrow(df),3)
df[random_na_index,demand := NA]
setorder(df,store,week)
store week demand
1: A 3 19.18
2: A 5 NA
3: A 6 NA
4: A 8 19.55
5: A 9 20.50
6: A 10 NA
7: B 1 20.75
8: B 2 17.70
9: B 4 19.40
10: B 7 17.52
我需要使用當前周之前的 2 周來計算移動平均線。 我做不到,因為zoo
和data.table
的 frollmean 在計算移動平均值時也使用當前行。 我也不知道如何在應用滾動 function 時處理NA
。
所需的 output 應如下所示;
store week demand desired_column
1: A 3 19.18 NA
2: A 5 NA 19.180
3: A 6 NA 19.180
4: A 8 19.55 NA
5: A 9 20.50 19.550
6: A 10 NA 20.025
7: B 1 20.75 NA
8: B 2 17.70 20.750
9: B 4 19.40 19.225
10: B 7 17.52 18.550
您可以在使用na.rm = TRUE
參數應用frollmean
之前shift
值:
df[order(store,week),desired:=frollmean(shift(demand),n=2,na.rm=T),by=.(store)][]
store week demand desired
<char> <int> <num> <num>
1: A 3 19.18 NA
2: A 5 NA 19.180
3: A 6 NA 19.180
4: A 8 19.55 NaN
5: A 9 20.50 19.550
6: A 10 NA 20.025
7: B 1 20.75 NA
8: B 2 17.70 20.750
9: B 4 19.40 19.225
10: B 7 17.52 18.550
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