Function not changing the data frame - r

Question

I've recently made a simple for loop that outputs the Max and Min of the past 5 prices and it works perfectly, creating 2 new columns showing MaxH and MinL:
for(i in 5:nrow(XBTUSD_df_s)){
XBTUSD_df_s$MaxH[i] = max(XBTUSD_df_s$Price[(i-(5-1)):i])
XBTUSD_df_s$MinL[i] = min(XBTUSD_df_s$Price[(i-(5-1)):i])
}
I then put this for loop into a function so that I can adjust how many prices I want the Max and Min to be based off like so (the print lines were added as a sanity check):
FindMaxMin = function(x){
for(i in x:nrow(XBTUSD_df_s)){
XBTUSD_df_s$MaxH[i] = max(XBTUSD_df_s$Price[(i-(x-1)):i])
XBTUSD_df_s$MinL[i] = min(XBTUSD_df_s$Price[(i-(x-1)):i])
print(XBTUSD_df_s$MaxH[i])
print(XBTUSD_df_s$MinL[i])
}
}
But after for example:
FindMaxMin(x = 10)
The console will spit out all the expected results but unlike the for loop by itself, my dataframe will not automatically add on the MaxH and MinL columns.
I've tried return() and I think most likely it is a global environment problem but can't seem to wrap my head around it.
Thanks in advance!

Answer 1

You need to return the object from the function and then assign it later:
FindMaxMin = function(x, XBTUSD_df_s){
for(i in x:nrow(XBTUSD_df_s)){
XBTUSD_df_s$MaxH[i] = max(XBTUSD_df_s$Price[(i-(x-1)):i])
XBTUSD_df_s$MinL[i] = min(XBTUSD_df_s$Price[(i-(x-1)):i])
print(XBTUSD_df_s$MaxH[i])
print(XBTUSD_df_s$MinL[i])
}
return (XBTUSD_df_s)
}
new = FindMaxMin(10, XBTUSD_df_s)