如何寫R代表環瓦特/變量值替換

Question

問題：

V是與多個NAS的載體。編寫一個函數來替換這些NA值，使得在索引i處的缺失值應該由在索引p和q處的非NA值的平均值代替，其中| p - i | + | q - i |被最小化。

所以，如果我的矢量("NA", 1, 2, "NA", "NA", 3)那麼我的結果必須是(1.5, 1, 2, 1.5, 1.5, 3)

我如何寫一個嵌套的for循環來產生這種輸出？

Answer 1

dist_elem <- function(x,pos){ 
    # Function that calculates the distance between pos and all other positions in vector x 
    d <- rep(0,length(x)) 
    for (i in 1:length(x)){ 
    d[i] <- abs(pos - i) 
    } 
    return(d) 
} 


for (i in 1:length(x)){ 

    if (is.na(x[i])){ 
    # distances between all other elements 
    distances <- dist_elem(x,i) 
    # NA for that element 
    distances[distances == 0] <- NA 
    # NA for the NAs 
    distances[is.na(x)] <- NA 
    # Sort and get the first two lower distances 
    s <- sort(distances)[1:2] 
    # The closest element (first of that vector in case of ties) 
    x1 <- x[which(distances == s[1])[1]] 
    # The second closest element (first of that vector in case of ties) 
    x2 <- x[which(distances == s[2])[1]] 

    out <- (x1 + x2)/2 

    x[i] <- out 
    } 

} 

Answer 2

您可以使用此一：

vect <- c(NA, 1, 2, NA, NA, 3) 
flag <- is.na(vect)+0 
wh <- which(is.na(vect)==1) 
flag[flag==1] <- wh 
#flag is a container of all values, however a missing vector position will contain a value of 0 a non missing value will contain the position 
k <- 0 
#a rolling itertor which changes the mean as per the non missing values in the vector 
vect_ <- vect 
# Final vector which will have the outcome. 
for(i in 1:(length(vect))){ 
    k <- ifelse(flag[i] > 0 , k+1,k) 
    k <- ifelse(k == length(wh), k-1,k) 
vect_[i] <- ifelse(flag[i] > 0, 
        mean(vect[min(wh):diff(c(1,wh[1+k]))],na.rm=T),vect[i]) 
} 

vect_ 

> vect_ 
[1] 1.5 1.0 2.0 1.5 1.5 3.0