Conditional subsetting of a data frame R - r

Question

Let the data frame be:
set.seed(123)
df<-data.frame(name=sample(LETTERS,260,replace=TRUE),
hobby=rep(c("outdoor","indoor"),260),chess=rnorm(1:10))
and the condition which I will use to extract from df be:
df_cond<-df %>% group_by(name,hobby) %>%
summarize(count=n()) %>%
mutate(sum.var=sum(count),sum.name=length(name)) %>%
filter(sum.name==2) %>%
mutate(min.var=min(count)) %>%
mutate(use=ifelse(min.var==count,"yes","no")) %>%
filter(grepl("yes",use))
I want to randomly extract the rows from df that correspond to the (name,hobby,count) combination in df_cond along with the rest of df. I am having bit of a trouble combining %in% and sample.Thanks for any clue!
Edit: For example:
head(df_cond)
name hobby count sum.var sum.name min.var use
<fctr> <fctr> <int> <int> <int> <int> <chr>
1 A indoor 2 6 2 2 yes
2 B indoor 8 16 2 8 yes
3 B outdoor 8 16 2 8 yes
4 C outdoor 6 14 2 6 yes
5 D indoor 10 24 2 10 yes
6 E outdoor 8 18 2 8 yes
Using the above data frame, I want to randomly extract 2 rows (=count) with the combination A+indoor(row1) from df,
8 rows with the combination B+indoor (row 2) from df ....and so on.
Combining #denrous and #Jacob answers to get what I need. like so:
m2<-df_cond %>%
mutate(data = map2(name, hobby, function(x, y) {df %>% filter(name == x, hobby == y)})) %>%
ungroup() %>%
select(data) %>%
unnest()
test<-m2 %>%
group_by(name,hobby) %>%
summarize(num.levels=length(unique(hobby))) %>%
ungroup() %>%
group_by(name) %>%
summarize(total_levels=sum(num.levels)) %>%
filter(total_levels>1)
fin<-semi_join(m2,test)

Answer 1

If I understand correctly, you could use purrr to achieve what you want:
df_cond %>%
mutate(data = map2(name, hobby, function(x, y) {filter(df, name == x, hobby == y)})) %>%
mutate(data = map2(data, count, function(x, y) sample_n(x, size = y)))
And if you want the same form as df:
df_cond %>%
mutate(data = map2(name, hobby, function(x, y) {df %>% filter(name == x, hobby == y)})) %>%
mutate(data = map2(data, count, function(x, y) sample_n(x, size = y))) %>%
ungroup() %>%
select(data) %>%
unnest()

Answer 2

Edited based on OP clarification.
There has to better way but I'd use a loop:
library(dplyr)
master_df <- data.frame()
for (i in 1:nrow(df_cond)){
name = as.character(df_cond[i, 1])
hobby = as.character(df_cond[i, 2])
n = as.numeric(df_cond[i, 3])
temp_df <- df %>% filter(name == name, hobby == hobby)
temp_df <- sample_n(temp_df, n)
master_df <- rbind(master_df, temp_df)
}

Answer 3

Not clear if this is exactly what you want, but you may be looking for left_join:
df %>%
left_join(df_cond, by = "name")