r - fill columns in data frame

问题

    V1 V2 V3
1   a  b  c 
2   a  d  c 
3   a  b  g
4   f  b  c 
5   a  b  c 
6   a  b  c 
7   a  b  c

I want to fill columns in data frame with values from rows above. It should look like this.

    V1 V2 V3
1   a  b  c 
2   a  d  c 
3   a  d  g
4   f  d  g 
5   f  d  g 
6   f  d  g 
7   f  d  g

回答1:

rollapply from the package zoo does this. Here the window is given as the entire set. partial=TRUE is used so you get intermediate results.

rollapplyr(df, nrow(df), max, partial=TRUE)
##      V1  V2  V3 
## [1,] "a" "b" "c"
## [2,] "a" "d" "c"
## [3,] "a" "d" "g"
## [4,] "f" "d" "g"
## [5,] "f" "d" "g"
## [6,] "f" "d" "g"
## [7,] "f" "d" "g"

rollapplyr sets align = 'right'. Note that this does produce a matrix as a result.

回答2:

We can use base R methods for this

df1[] <- lapply(df1, function(x) {x1 <- factor(x)
                 levels(x1)[cummax(as.integer(x1))]})
df1
#  V1 V2 V3
#1  a  b  c
#2  a  d  c
#3  a  d  g
#4  f  d  g
#5  f  d  g
#6  f  d  g
#7  f  d  g

回答3:

I would use a for-loop for this.

Here's a very manual approach that computes the indexes of the breaks in value along the vector (unconditionally taking the first element as a pseudo-break), gets the index NL from the last where NL allows us to parameterize the run-length that will be used to fill subsequent run-lengths, and finally assigns over subsequent run-lengths the value from the selected run-length.

NL <- 2L;
for (ci in seq_len(ncol(df))) {
    x <- c(1L,which(df[-1L,ci]!=df[-nrow(df),ci])+1L);
    i <- x[max(1L,length(x)-NL+1L)];
    df[i:nrow(df),ci] <- df[i,ci];
}; ## end for
df;
##   V1 V2 V3
## 1  a  b  c
## 2  a  d  c
## 3  a  d  g
## 4  f  d  g
## 5  f  d  g
## 6  f  d  g
## 7  f  d  g

Data

df <- data.frame(V1=c('a','a','a','f','a','a','a'),V2=c('b','d','b','b','b','b','b'),V3=c('c'
,'c','g','c','c','c','c'),stringsAsFactors=F);

回答4:

Here's another solution using cumany in dplyr:

library(dplyr)

df %>%
  mutate_all(funs(ifelse(cumany(. == max(.)), max(.), .)))

Result:

  V1 V2 V3
1  a  b  c
2  a  d  c
3  a  d  g
4  f  d  g
5  f  d  g
6  f  d  g
7  f  d  g

来源：https://stackoverflow.com/questions/38064415/r-fill-columns-in-data-frame

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