Simple nested for loop issue

Question

While trying to implement nested for loops in a large dataframe, I realized that the nested for loops are not producing the results I expect. Here's an extract of my problem.

df <- data.frame(nrow = 20, ncol = 1)
df <- data.frame(  LastPrice = c( 1221, 1220, 1220, 1217, 1216,  1218 , 1216, 1216, 1217, 1220, 1219, 1218, 1220, 1216, 1217, 1218, 1218, 1207, 1206, 1205))
for(j in 1:20) {for (i in 1:10) {df$SignalBinary[j] <- ifelse (df$LastPrice[j+i] == 1216, 1, 0)}}

I would expect and want the nested for loops to add SignalBinary vector to df dataframe with the following values: "1 1 1 1 1 1 1 1 1 1 NA NA NA NA NA NA NA NA NA NA"

"1" on first 10 rows because 1216 is present for each in at least one of the 10 rows below
"NA" on following 10 because for those the i loop extends outside the vector length

Instead, df$SignalBinary becomes "0 0 0 1 0 0 0 0 0 0 NA NA NA NA NA NA NA NA NA NA"

Don't get it. Why is it registering only one 1216? Thank you very much!

What is your first line for? And also, what do you mean by because 1216 is present for each in at least one of the 10 rows below? Below what? Do you mean if 1216 is present in rows 11-20? — Rich Scriven
– Rich Scriven, Commented Apr 14, 2016 at 22:22
Guess first line not necessary. Meant present at least once in rows 02-11 for recording a 1 in row 1, at least once in rows 03-12 for recording a 1 in row 2 ... and at least once in rows 11-20 for recording a 1 in row 10. Thanks. — Krug
– Krug, Commented Apr 14, 2016 at 22:44

HubertL · Accepted Answer · 2016-04-14 22:36:27Z

1

You forget to sum up in the second loop, so it only matches when the last one i is 2016. Try this:

for(j in 1:20) {
    tmp <- 0
    for (i in 1:10) 
        tmp <- tmp + ifelse(df$LastPrice[j+i] == 1216, 1, 0)
    df$SignalBinary[j] <- as.integer(tmp>0)
}

Or without a temp variable:

df$SignalBinary[j] <- 0
for(j in 1:20) {
    for(i in 1:10) 
        df$SignalBinary[j] <- as.integer(df$SignalBinary[j] || ifelse (df$LastPrice[j+i] == 1216, 1, 0));
        }

edited Apr 14, 2016 at 22:36

answered Apr 14, 2016 at 22:30

HubertL

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1 Comment

Krug Over a year ago

I'm humbled. Thank you!

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