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
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
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)
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)
in fact. use the methods of vector and index. we can also achieve the same result, and more easier to understand:
rawdata <- data.frame('time' = 1:3,
'x1' = 4:6,
'x2' = 7:9,
'x3' = 10:12)
rawdata[rep(1, time=2), ] %>% remove_rownames()
# time x1 x2 x3
# 1 1 4 7 10
# 2 1 4 7 10
@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$freq), 1:2]
The code for data.table is a tad cleaner:
# convert to data.table by reference
setDT(df)
df.expanded <- df[rep(seq(.N), freq), !"freq"]
I know this is not the case but if you need to keep the original freq column, you can use another tidyverse approach together with rep:
library(purrr)
df <- data.frame(var1 = c('a', 'b', 'c'), var2 = c('d', 'e', 'f'), freq = 1:3)
df %>%
map_df(., rep, .$freq)
#> # A tibble: 6 x 3
#> var1 var2 freq
#> <fct> <fct> <int>
#> 1 a d 1
#> 2 b e 2
#> 3 b e 2
#> 4 c f 3
#> 5 c f 3
#> 6 c f 3
Created on 2019-12-21 by the reprex package (v0.3.0)
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
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
Source: Stackoverflow.com