按組遞增

Question

我試圖爲每組增加一列。所以如果有價值，那麼我們會根據它之前的價值來增加它，否則我們就放棄它。

因此，例如，它會從df到dfb。

df <- data.frame(group = c("A", "A", "B", "B", "B", "C", "C", "C", "D", "D"), 
       num = c(1, NA, NA, 8, NA, 5, NA, NA, 10, NA)) 
dfb <- data.frame(group = c("A", "A", "B", "B", "B", "C", "C", "C", "D", "D"), 
       num = c(1, 2, NA, 8, 9, 5, 6, 7, 10, 11)) 
> df 

    group num 
1  A 1 
2  A NA 
3  B NA 
4  B 8 
5  B NA 
6  C 5 
7  C NA 
8  C NA 
9  D 10 
10  D NA 

> dfb 
    group num 
1  A 1 
2  A 2 
3  B NA 
4  B 8 
5  B 9 
6  C 5 
7  C 6 
8  C 7 
9  D 10 
10  D 11 

我最好的嘗試是這一點，但

dfc <- df %>% 
    mutate(num = ifelse(is.na(num),lag(num) + 1, num)) 

刪除我剛纔的問題，因爲以前不好界定我的問題，它沒有工作。 感謝您的幫助！

Answer 1

我們可以做

df %>% 
group_by(grp1= cumsum(!is.na(num)), group) %>% 
mutate(num = if(n() > 1) num[1L] + row_number()-1 else num) %>% 
ungroup() %>% 
select(-grp1) 
# A tibble: 10 × 2 
# group num 
# <fctr> <dbl> 
#1  A  1 
#2  A  2 
#3  B NA 
#4  B  8 
#5  B  9 
#6  C  5 
#7  C  6 
#8  C  7 
#9  D 10 
#10  D 11 

---

或用data.table

library(data.table) 
setDT(df)[, num := if(.N >1) num[1L] + seq_len(.N)-1 
      else num,.(grp1=cumsum(!is.na(num)), group)] 

Answer 2

你需要的一切都爲循環:)歡呼一個基本的！

df <- data.frame(group = c("A", "A", "B", "B", "B", "C", "C", "C", "D", "D"), 
       num = c(1, NA, NA, 8, NA, 5, NA, NA, 10, NA)) 
df.new <- df 

for(i in 2:dim(df.new)[1]){ 

    if(!is.na(df[i - 1, 'num'])){ 

    df.new[i, 'num'] <- df[i - 1, "num"] + 1 

    }