R-循环每一行，并用前一行的值填充

我想测试特定列中的值是否包含NA值，如果是，则用前一行中的值填充NA空间。我仍在努力掌握

apply

函数系列的诀窍

例如，我想把这个：

      Date   Balance
2012-01-01      1000
2012-01-02        NA
2012-01-03        NA
2012-01-04      1200
2012-01-05      1215
2012-01-06        NA

进入：

---

这是zoo软件包中的

na.locf

函数的任务。请参见

？na.locf

考虑

DF

是您的data.frame，然后：

DF <- read.table(text="      Date   Balance
2012-01-01      1000
2012-01-02        NA
2012-01-03        NA
2012-01-04      1200
2012-01-05      1215
2012-01-06        NA", header=TRUE)

library(zoo)
na.locf(DF)
        Date Balance
1 2012-01-01    1000
2 2012-01-02    1000
3 2012-01-03    1000
4 2012-01-04    1200
5 2012-01-05    1215
6 2012-01-06    1215

---

DF使用
data.table
和
roll=TRUE
也很好地做到了这一点

require(data.table)
# convert Date column to date format
df$Date <- as.Date(df$Date)
# keep this, as we'll remove rows with NA to use `roll`
dates   <- df$Date
# remove rows with NA
dt2     <- na.omit(data.table(df))
# set key to Date
setkey(dt2, "Date")
# use dates which has the NA rows that will be filled 
# with value from previous column with roll=T
dt2[J(dates), roll=T]

#          Date Balance
# 1: 2012-01-01    1000
# 2: 2012-01-02    1000
# 3: 2012-01-03    1000
# 4: 2012-01-04    1200
# 5: 2012-01-05    1215
# 6: 2012-01-06    1215

require（data.table）
#将日期列转换为日期格式
df$Date查看动物园包装good find@Jilber中的
na.locf
。
apply
系列在这里不起作用，因为您想要对给定值执行的操作取决于附近的值（即，您不能在
apply
函数中使用索引）。最简单的
base
方法可能是
for
循环（如果我错了请纠正我）：
for（i in 1:length（DF$Balance））if（is.na（DF$余额[i]）DF$余额[i]=DF$余额[i-1]
require(data.table)
# convert Date column to date format
df$Date <- as.Date(df$Date)
# keep this, as we'll remove rows with NA to use `roll`
dates   <- df$Date
# remove rows with NA
dt2     <- na.omit(data.table(df))
# set key to Date
setkey(dt2, "Date")
# use dates which has the NA rows that will be filled 
# with value from previous column with roll=T
dt2[J(dates), roll=T]

#          Date Balance
# 1: 2012-01-01    1000
# 2: 2012-01-02    1000
# 3: 2012-01-03    1000
# 4: 2012-01-04    1200
# 5: 2012-01-05    1215
# 6: 2012-01-06    1215