Question

我有一个更大的现有数据框架。对于这个较小的例子，我想根据第＆＃34列首先用newstate（df2）替换一些变量（替换state（df1））。＆＃34;我的问题是值返回为NA，因为只有一些名称在新数据帧（df2）中匹配。

现有数据框：

state = c("CA","WA","OR","AZ")
first = c("Jim","Mick","Paul","Ron")
df1 <- data.frame(first, state)

      first state
    1   Jim    CA
    2  Mick    WA
    3  Paul    OR
    4   Ron    AZ

与现有数据框匹配的新数据框

state = c("CA","WA")
newstate = c("TX", "LA")
first =c("Jim","Mick")
df2 <- data.frame(first, state, newstate)

  first state newstate
1   Jim    CA       TX
2  Mick    WA       LA

尝试使用匹配，但返回NA为＆＃34;状态＆＃34;匹配＆＃34;第一＆＃34;在原始数据帧中找不到df2的变量。

df1$state <- df2$newstate[match(df1$first, df2$first)]

  first state
1   Jim    TX
2  Mick    LA
3  Paul  <NA>
4   Ron  <NA>

有没有办法忽略nomatch或nomatch按原样返回现有变量？这将是期望结果的例子：吉姆/米克的状态被更新，而保罗和罗恩的状态不会改变。

      first state
    1   Jim    TX
    2  Mick    LA
    3  Paul    OR
    4   Ron    AZ

Answer 1

这就是你想要的;除非你真的想要使用因子，否则在你的data.frame调用中使用stringsAsFactors = FALSE。注意在匹配调用中使用nomatch = 0.

> state = c("CA","WA","OR","AZ")
> first = c("Jim","Mick","Paul","Ron")
> df1 <- data.frame(first, state, stringsAsFactors = FALSE)
> state = c("CA","WA")
> newstate = c("TX", "LA")
> first =c("Jim","Mick")
> df2 <- data.frame(first, state, newstate, stringsAsFactors = FALSE)
> df1
  first state
1   Jim    CA
2  Mick    WA
3  Paul    OR
4   Ron    AZ
> df2
  first state newstate
1   Jim    CA       TX
2  Mick    WA       LA
> 
> # create an index for the matches
> indx <- match(df1$first, df2$first, nomatch = 0)
> df1$state[indx != 0] <- df2$newstate[indx]
> df1
  first state
1   Jim    TX
2  Mick    LA
3  Paul    OR
4   Ron    AZ

Answer 2

我认为使用角色向量比使用因素更好。

> df1 <- data.frame(first, state,stringsAsFactors=FALSE)
> state = c("CA","WA")
> newstate = c("TX", "LA")
> first =c("Jim","Mick")
> df2 <- data.frame(first, state, newstate, stringsAsFactors=FALSE)
> df1[ match(df2$first, df1$first ), "state"] <- df2$newstate
> df1
  first state
1   Jim    TX
2  Mick    LA
3  Paul    OR
4   Ron    AZ

Answer 3

library(data.table)
DT1 <- as.data.table(df1)
DT2 <- as.data.table(df2)


setkey(DT1, first, state)
setkey(DT2, first, state)

DT1[DT2]
#    first state newstate
# 1:   Jim    CA       TX
# 2:  Mick    WA       LA

请注意[.data.table也有一个nomatch参数，即：

DT2[DT1, nomatch=0]
#    first state newstate
# 1:   Jim    CA       TX
# 2:  Mick    WA       LA

DT2[DT1, nomatch=NA]
#    first state newstate
# 1:   Jim    CA       TX
# 2:  Mick    WA       LA
# 3:  Paul    OR       NA
# 4:   Ron    AZ       NA

使用R中的匹配函数，具有无匹配的返回值

3 个答案: