Putting rows from old data frame into a new data frame - r

Question

I have my code:
new_df = data.frame()
#G = 0
for (i in 1:nrow(furin_data)){
frac = furin_data[i,3]/furin_data[i,5]
#print(frac)
if (frac > 2 || frac < 0.5) {
name = furin_data[i,1]
print(name)
new_df = furin_data[i,]
#print(new_df)
#G = G + 1
}
write.csv(new_df, "C:\\User\\Documents\\MyData.csv", row.names = FALSE)
}
It creates a new data file, but only the last row is written and not all of the the rows based on the condition. I cannot seem to figure out where is the problem.

Answer 1

That's because you're assigning the row to it, so every assignment overrides the previous one. What you want is to add rows to it instead.
new_df[nrow(new_df)+1,] = furin_data[i,]
Another thing is that you created your new_df data frame without any columns, so none are assigned in the transfer. You should define it with the same types and names of columns as furin_data, so those columns could be copied. An easy of initializing it as empty but having the same structure would be:
new_df = furin_data[F,]
Buuut, in the R language, writing a loop is not the best way to do things. R is a vectorized language, meaning it can perform all operations on a vector at once, causing it to execute much much faster. So a conversion of your whole code to R style would be:
library(dplyr)
new_df <-
furin_data %>%
mutate(frac = .[3] / .[5]) %>%
subset(frac > 2 | frac < 0.5)
write.csv(new_df, "C:\\User\\Documents\\MyData.csv", row.names = FALSE)