CODEWITHSUNDEEP
raggregatetapply
wkde
wkde

Reputation: 453

group by a dataframe and get a row of specific index within each group in r

I have a df like

ProjectID Dist
  1        x
  1        y
  2        z
  2        x
  2        h
  3        k
  ....     ....

and a vector of indices of lengthunique(df$ProjectID) like

  2        
  3        
  1        
  ....

I would like to get Dist by ProjectID whose index is the element vector corresponding to project ID. So the result I want looks like

ProjectID Dist
  1        y
  2        h
  3        k
  ....     ....

I tried

aggregate(XRKL ~ ID, FUN=..?, data=df)

but I'm not sure where I can put the vector of indices. Is there a way to get the right result from dply ftns, tapply, or aggregate? Or do I need to make a function of my own? Thank you.

Upvotes: 0

Views: 439

Answers (1)

Ronak Shah
Ronak Shah

Reputation: 389055

You can add the indices in the dataframe itself and then select that row from each group.

inds <- c(2, 3, 1)

df %>%
  mutate(inds = inds[match(ProjectID, unique(ProjectID))]) %>%
  #If ProjectID is sequential like 1, 2, 3
  #mutate(inds = inds[ProjectID]) %>%
  group_by(ProjectID) %>%
  slice(first(inds)) %>%
  ungroup() %>%
  select(-inds)

#  ProjectID Dist 
#      <int> <chr>
#1         1 y    
#2         2 h    
#3         3 k

data

df <- structure(list(ProjectID = c(1L, 1L, 2L, 2L, 2L, 3L), Dist = c("x", 
"y", "z", "x", "h", "k")), class = "data.frame", row.names = c(NA, -6L))

Upvotes: 1

Related Questions