Repeat each row of data.frame the number of times specified in a column

问题

df <- data.frame(var1 = c('a', 'b', 'c'), var2 = c('d', 'e', 'f'),
                 freq = 1:3)

What is the simplest way to expand each row the first two columns of the data.frame above, so that each row is repeated the number of times specified in the column 'freq'?

In other words, go from this:

df
  var1 var2 freq
1    a    d    1
2    b    e    2
3    c    f    3

To this:

df.expanded
  var1 var2
1    a    d
2    b    e
3    b    e
4    c    f
5    c    f
6    c    f

回答1:

Here's one solution:

df.expanded <- df[rep(row.names(df), df$freq), 1:2]

Result:

    var1 var2
1      a    d
2      b    e
2.1    b    e
3      c    f
3.1    c    f
3.2    c    f

回答2:

old question, new verb in tidyverse:

library(tidyr) # version >= 0.8.0
df <- data.frame(var1=c('a', 'b', 'c'), var2=c('d', 'e', 'f'), freq=1:3)
df %>% 
  uncount(freq)

    var1 var2
1      a    d
2      b    e
2.1    b    e
3      c    f
3.1    c    f
3.2    c    f

回答3:

Use expandRows() from the splitstackshape package:

library(splitstackshape)
expandRows(df, "freq")

Simple syntax, very fast, works on data.frame or data.table.

Result:

    var1 var2
1      a    d
2      b    e
2.1    b    e
3      c    f
3.1    c    f
3.2    c    f

回答4:

@neilfws's solution works great for data.frames, but not for data.tables since they lack the row.names property. This approach works for both:

df.expanded <- df[rep(seq(nrow(df)), df$freq), 1:2]

The code for data.table is a tad cleaner:

# convert to data.table by reference
setDT(df)
df.expanded <- df[rep(seq(.N), freq), !"freq"]

回答5:

In case you have to do this operation on very large data.frames I would recommend converting it into a data.table and use the following, which should run much faster:

library(data.table)
dt <- data.table(df)
dt.expanded <- dt[ ,list(freq=rep(1,freq)),by=c("var1","var2")]
dt.expanded[ ,freq := NULL]
dt.expanded

See how much faster this solution is:

df <- data.frame(var1=1:2e3, var2=1:2e3, freq=1:2e3)
system.time(df.exp <- df[rep(row.names(df), df$freq), 1:2])
##    user  system elapsed 
##    4.57    0.00    4.56
dt <- data.table(df)
system.time(dt.expanded <- dt[ ,list(freq=rep(1,freq)),by=c("var1","var2")])
##    user  system elapsed 
##    0.05    0.01    0.06

回答6:

Another dplyr alternative with slice where we repeat each row number freq times

library(dplyr)

df %>%  
  slice(rep(seq_len(n()), freq)) %>% 
  select(-freq)

#  var1 var2
#1    a    d
#2    b    e
#3    b    e
#4    c    f
#5    c    f
#6    c    f

seq_len(n()) part can be replaced with any of the following.

df %>% slice(rep(1:nrow(df), freq)) %>% select(-freq)
#Or
df %>% slice(rep(row_number(), freq)) %>% select(-freq)
#Or
df %>% slice(rep(seq_len(nrow(.)), freq)) %>% select(-freq)

回答7:

Another possibility is using tidyr::expand:

library(dplyr)
library(tidyr)

df %>% group_by_at(vars(-freq)) %>% expand(temp = 1:freq) %>% select(-temp)

#> # A tibble: 6 x 2
#> # Groups:   var1, var2 [3]
#>   var1  var2 
#>   <fct> <fct>
#> 1 a     d    
#> 2 b     e    
#> 3 b     e    
#> 4 c     f    
#> 5 c     f    
#> 6 c     f

One-liner version of vonjd's answer:

library(data.table)

setDT(df)[ ,list(freq=rep(1,freq)),by=c("var1","var2")][ ,freq := NULL][]

#>    var1 var2
#> 1:    a    d
#> 2:    b    e
#> 3:    b    e
#> 4:    c    f
#> 5:    c    f
#> 6:    c    f

^{Created on 2019-05-21 by the reprex package (v0.2.1)}

来源：https://stackoverflow.com/questions/2894775/repeat-each-row-of-data-frame-the-number-of-times-specified-in-a-column

标签

dataframe

replicate