Question

I'm an unexperienced user of R and I need to create quite a complicated stuff. My dataset looks like this :

a,b,c,d,e are different individuals. I want to complete the D column as follows : At the last line for each individual in the col A, D = sum(C)/(B-1).

Expected results should look like :

results

D4=sum(C2:C4)/(B4-1)=0.5

D6=sum(C5:C6)/(B6-1)=1, etc.

I attempted to deal with it with something like :

for(i in 2:NROW(dataset)){
  dataset[i,4]<-ifelse(
   (dataset[i,1]==data1[i-1,1]),sum(dataset[i,3])/(dataset[i,2]-1),NA
  )
}

But it is obviously not sufficient, as it computes the D value for all the rows and not only the last for each individual, and it does not calculate the sum of C values for this individual.

And I really don't know how to figure it out. Do you guys have any advice ? Many thanks.

Answer 1

如果我理解你的问题，那么这是达到预期结果的一种方法：

df <- data.frame(
A=c("a","a","a","b","b","c","c","c","d","e","e"),
B=c(3,3,3,2,2,3,3,3,1,2,2),
C=c(NA,1,0,NA,1,NA,0,1,NA,NA,0), 
stringsAsFactors = FALSE)

for(i in 2:NROW(df)){
  df[i,4]<-ifelse(
    (df[i,1]!=df[i+1,1] | i == nrow(df)),sum(df[df$A == df[i,1],]$C, na.rm=TRUE)/(df[i,2]-1),NA
  )
}

此代码生成下表：

   A B  C  V4
1  a 3 NA  NA
2  a 3  1  NA
3  a 3  0 0.5
4  b 2 NA  NA
5  b 2  1 1.0
6  c 3 NA  NA
7  c 3  0  NA
8  c 3  1 0.5
9  d 1 NA NaN
10 e 2 NA  NA
11 e 2  0 0.0

ifelse首先测试A列当前行的个体是否与下一行中的个体不同，或者它是否是最后一行。

如果它是这个个体的最后一行，它将获取行的列C（忽略NA）与A列中存在的个体除以B列中的值减1。

否则它会在第四列中放置NA。

Answer 2

使用dplyr您可以尝试为所有行生成D，然后删除不需要的地方：

dftest %>%
  group_by(A,B) %>%
  dplyr::mutate(D = sum(C, na.rm=TRUE)/(B-1)) %>%
  dplyr::mutate(D = if_else(row_number()== n(), D, as.double(NA)))

给出：

Source: local data frame [11 x 4]
Groups: A, B [5]

       A     B     C     D
   <chr> <dbl> <dbl> <dbl>
1      a     3    NA    NA
2      a     3     1    NA
3      a     3     0   0.5
4      b     2    NA    NA
5      b     2     1   1.0
6      c     3    NA    NA
7      c     3     0    NA
8      c     3     1   0.5
9      d     1    NA   NaN
10     e     2    NA    NA
11     e     2     0   0.0

Create a counter in a for loop in R

2 个答案: