Sampling randomly and non-randomly in one sample

Is there a way to sample X number of random rows and X non-random rows in a single sample?
For example, I want to get 1,000 samples of 4 rows of iris. I want to randomly sample 3 rows of iris and the fourth row will be the same one in each sample (this is to mimic a hybrid sampling design).

I can sample 3 random rows 1000x and the fixed row 1000x and then merge the two data frames together, but for a few reasons this is not an ideal situation. The code to do that looks something like the following:

df<- iris

fixed_sample<- iris[7,]

random<- list()
fixed<- list()

counter<- 0
for (i in 1:1000) {
  # sample 4 randomly selected transects 100 time
  tempsample_random<- df[sample(1:nrow(df), 3, replace=F),]
  tempsample_fixed<- fixed_sample[sample(1:nrow(fixed_sample), 1, replace=F), ]
  
  random[[i]]=tempsample_random
  fixed[[i]]=tempsample_fixed
  
  
  counter<- counter+1
  print(counter)
}


random_results<- do.call(rbind, random)
fixed_results<- do.call(rbind, fixed)

From here I would make a new column as a grouping variable and then merge them together based on that group. So every four rows of the final data frame has 3 random rows and row number 7 (fixed_sample) in each sample.

I’ve looked into using splitstackshape::stratified, but haven’t gotten it to work the way I need it to. I’ll be doing this over several levels of sampling effort (sample 2, 3, 4, 5 rows, etc. 1,000x each) so it would be ideal to be able to pull the fixed and random rows in the same sample from the beginning.

Any help would be greatly appreciated.

>Solution :

I think you can do this in a single line using lapply. In this case we will draw 3 samples, but you can change seq(3) to seq(1000) to get your 1000 samples. I have followed your example and selected row 7 as the fixed row.

lapply(seq(3), function(i) iris[c(sample(seq(nrow(iris))[-7], 3), 7),])
#> [[1]]
#>     Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
#> 67           5.6         3.0          4.5         1.5 versicolor
#> 105          6.5         3.0          5.8         2.2  virginica
#> 111          6.5         3.2          5.1         2.0  virginica
#> 7            4.6         3.4          1.4         0.3     setosa
#> 
#> [[2]]
#>     Sepal.Length Sepal.Width Petal.Length Petal.Width   Species
#> 147          6.3         2.5          5.0         1.9 virginica
#> 131          7.4         2.8          6.1         1.9 virginica
#> 126          7.2         3.2          6.0         1.8 virginica
#> 7            4.6         3.4          1.4         0.3    setosa
#> 
#> [[3]]
#>     Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
#> 143          5.8         2.7          5.1         1.9  virginica
#> 145          6.7         3.3          5.7         2.5  virginica
#> 60           5.2         2.7          3.9         1.4 versicolor
#> 7            4.6         3.4          1.4         0.3     setosa

^{Created on 2022-05-18 by the reprex package (v2.0.1)}