问题
I already made a similar question but now I want just to restrict the new values of NA.
I have some data like this:
Date 1 Date 2 Date 3 Date 4 Date 5 Date 6
A NA 0.1 0.2 NA 0.3 0.2
B 0.1 NA NA 0.3 0.2 0.1
C NA NA NA NA 0.3 NA
D 0.1 0.2 0.3 NA 0.1 NA
E NA NA 0.1 0.2 0.1 0.3
I would like to change the NA values of my data based on the first date a value is registered. So for example for A, the first registration is Date 2. Then I want that before that registration the values of NA in A are 0, and after the first registration the values of NA become the mean of the nearest values (mean of date 3 and 5).
In case the last value is an NA, transform it into the last registered value (as in C and D). In the case of E all NA values will become 0.
Get something like this:
Date 1 Date 2 Date 3 Date 4 Date 5 Date 6
A 0 0.1 0.2 0.25 0.3 0.2
B 0.1 0.2 0.2 0.3 0.2 0.1
C 0 0 0 0 0.3 0.3
D 0.1 0.2 0.3 0.2 0.1 0.1
E 0 0 0.1 0.2 0.1 0.3
Can you help me? I'm not sure how to do it in R.
回答1:
Here is a way using na.approx from the zoo package and apply with MARGIN = 1 (so this is probably not very efficient but get's the job done).
library(zoo)
df1 <- as.data.frame(t(apply(dat, 1, na.approx, method = "constant", f = .5, na.rm = FALSE)))
This results in
df1
# V1 V2 V3 V4 V5
#A NA 0.1 0.2 0.25 0.3
#B 0.1 0.2 0.2 0.30 0.2
#C NA NA NA NA 0.3
#E NA NA 0.1 0.20 0.1
Replace NAs and rename columns.
df1[is.na(df1)] <- 0
names(df1) <- names(dat)
df1
# Date_1 Date_2 Date_3 Date_4 Date_5
#A 0.0 0.1 0.2 0.25 0.3
#B 0.1 0.2 0.2 0.30 0.2
#C 0.0 0.0 0.0 0.00 0.3
#E 0.0 0.0 0.1 0.20 0.1
explanation
Given a vector
x <- c(0.1, NA, NA, 0.3, 0.2)
na.approx(x)
returns x with linear interpolated values
#[1] 0.1000000 0.1666667 0.2333333 0.3000000 0.2000000
But OP asked for constant values so we need the argument method = "constant" from the approx function.
na.approx(x, method = "constant")
# [1] 0.1 0.1 0.1 0.3 0.2
But this is still not what OP asked for because it carries the last observation forward while you want the mean for the closest non-NA values. Therefore we need the argument f (also from approx)
na.approx(x, method = "constant", f = .5)
# [1] 0.1 0.2 0.2 0.3 0.2 # looks good
From ?approx
f : for method = "constant" a number between 0 and 1 inclusive, indicating a compromise between left- and right-continuous step functions. If y0 and y1 are the values to the left and right of the point then the value is y0 if f == 0, y1 if f == 1, and y0*(1-f)+y1*f for intermediate values. In this way the result is right-continuous for f == 0 and left-continuous for f == 1, even for non-finite y values.
Lastly, if we don't want to replace the NAs at the beginning and end of each row we need na.rm = FALSE.
From ?na.approx
na.rm : logical. If the result of the (spline) interpolation still results in NAs, should these be removed?
data
dat <- structure(list(Date_1 = c(NA, 0.1, NA, NA), Date_2 = c(0.1, NA,
NA, NA), Date_3 = c(0.2, NA, NA, 0.1), Date_4 = c(NA, 0.3, NA,
0.2), Date_5 = c(0.3, 0.2, 0.3, 0.1)), .Names = c("Date_1", "Date_2",
"Date_3", "Date_4", "Date_5"), class = "data.frame", row.names = c("A",
"B", "C", "E"))
EDIT
If there are NAs in the last column we can replace these with the last non-NAs before we apply na.approx as shown above.
dat$Date_6[is.na(dat$Date_6)] <- dat[cbind(1:nrow(dat),
max.col(!is.na(dat), ties.method = "last"))][is.na(dat$Date_6)]
回答2:
This is another possible answer, using na.locf from the zoo package.
Edit: apply is actually not required; This solution fills in the last observed value if this value is missing.
# create the dataframe
Date1 <- c(NA,.1,NA,NA)
Date2 <- c(.1, NA,NA,NA)
Date3 <- c(.2,NA,NA,.1)
Date4 <- c(NA,.3,NA,.2)
Date5 <- c(.3,.2,.3,.1)
Date6 <- c(.1,NA,NA,NA)
df <- as.data.frame(cbind(Date1,Date2,Date3,Date4,Date5,Date6))
rownames(df) <- c('A','B','C','D')
> df
Date1 Date2 Date3 Date4 Date5 Date6
A NA 0.1 0.2 NA 0.3 0.1
B 0.1 NA NA 0.3 0.2 NA
C NA NA NA NA 0.3 NA
D NA NA 0.1 0.2 0.1 NA
# Load library
library(zoo)
df2 <- t(na.locf(t(df),na.rm = F)) # fill last observation carried forward
df3 <- t(na.locf(t(df),na.rm = F, fromLast = T)) # last obs carried backward
df4 <- (df2 + df3)/2 # mean of both dataframes
df4 <- t(na.locf(t(df4),na.rm = F)) # fill last observation carried forward
df4[is.na(df4)] <- 0 # NA values are 0
Date1 Date2 Date3 Date4 Date5 Date6
A 0.0 0.1 0.2 0.25 0.3 0.1
B 0.1 0.2 0.2 0.30 0.2 0.2
C 0.0 0.0 0.0 0.00 0.3 0.3
D 0.0 0.0 0.1 0.20 0.1 0.1
回答3:
Here's another option with base R + rollmean from zoo (clearly easy to rewrite in base R for this case with window size k = 2).
t(apply(df, 1, function(x) {
means <- c(0, rollmean(na.omit(x), 2), tail(na.omit(x), 1))
replace(x, is.na(x), means[1 + cumsum(!is.na(x))[is.na(x)]])
}))
# Date1 Date2 Date3 Date4 Date5 Date6
# A 0.0 0.1 0.2 0.25 0.3 0.2
# B 0.1 0.2 0.2 0.30 0.2 0.1
# C 0.0 0.0 0.0 0.00 0.3 0.3
# D 0.1 0.2 0.3 0.20 0.1 0.1
# E 0.0 0.0 0.1 0.20 0.1 0.3
Explanation. Suppose that x is the first row of df:
# Date1 Date2 Date3 Date4 Date5 Date6
# A NA 0.1 0.2 NA 0.3 0.2
Then
means
# [1] 0.00 0.15 0.25 0.25 0.20
is a vector of 0, rolling means of two the following non-NA elements, and the last non-NA element. Then all we need to do is to replace those elements of x that are is.na(x). We will replace them by the elements of means at indices 1 + cumsum(!is.na(x))[is.na(x)]. That's the trickier part. Here
cumsum(!is.na(x))
# [1] 0 1 2 2 3 4
Meaning that the first element of x has seen 0 non-NA elements, while, say, the last one has seen 4 non-NA elements so far. Then
cumsum(!is.na(x))[is.na(x)]
# [1] 0 2
is about those NA elements in x that we want to replace. Notice that then
1 + cumsum(!is.na(x))[is.na(x)]
# [1] 1 3
corresponds to the elements of means that we want to use for replacement.
回答4:
I am finding the function below too complicated but it works, so here it goes.
fun <- function(x){
if(anyNA(x)){
inx <- which(!is.na(x))
if(inx[1] > 1) x[seq_len(inx[1] - 1)] <- 0
prev <- inx[1]
for(i in inx[-1]){
if(i - prev > 1){
m <- mean(c(x[i], x[prev]))
while(prev < i){
x[prev] <- m
prev <- prev + 1
}
}
prev <- i
}
}
x
}
res <- t(apply(df1, 1, fun))
res <- as.data.frame(res)
res
# Date.1 Date.2 Date.3 Date.4 Date.5
#A 0.0 0.1 0.25 0.25 0.3
#B 0.2 0.2 0.20 0.30 0.2
#C 0.0 0.0 0.00 0.00 0.3
#E 0.0 0.0 0.10 0.20 0.1
Data.
df1 <- read.table(text = "
Date.1 Date.2 Date.3 Date.4 Date.5
A NA 0.1 0.2 NA 0.3
B 0.1 NA NA 0.3 0.2
C NA NA NA NA 0.3
E NA NA 0.1 0.2 0.1
", header = TRUE)
来源：https://stackoverflow.com/questions/54130682/transform-na-values-based-on-first-registration-and-nearest-values