Strange error: Error in if () { : missing value where TRUE/FALSE needed-CodePudding

I have the following data frame called studenti:

When I tried to run the following code:

maschi = data.frame()
indice = 0

for (i in seq_along(studenti$sesso)) {
    if (studenti$sesso[i] == "M") {
        indice = indice   1
        maschi[indice,] <- studenti[i,]
    }
}

the following error appeared "Error in if () { : missing value where TRUE/FALSE needed".

My goal is to copy in the data frame maschi only the rows of the data frame studenti such that sesso=M.

EDIT

EDIT: dput output

structure(list(sesso = c("F", "M", "M", "M", "M"), altezza = c(168, 
182, 176, 193, 178), peso = c(60, 75, 72, 95, 68), scarpe = c(41, 
43, 45, 45, 45), caso = c(7, 9, 5, 6, 7), matricola = c(1, -1, 
-1, -1, 6), mese = c(11, 5, 9, 5, 7), giorno = c(7, 2, 29, 8, 
12)), row.names = c(NA, 5L), class = "data.frame")

CodePudding user response：

It may be easier to use subset

maschi <- subset(studenti, sesso == "M")

or filter from dplyr

library(dplyr)
studenti %>%
     filter(sesso == "M")

The for loop can be done with rbind

maschi <- studenti[0,]
for(i in seq_len(nrow(studenti))) {
     if(studenti$sesso[i] == "M" & !is.na(studenti$sesso[i]))  {
        maschi <- rbind(maschi, studenti[i,])
   }
}

Also, in the OP's code, we just need

maschi <- studenti[0,]
indice = 0

for (i in seq_along(studenti$sesso)) {
    if (studenti$sesso[i] == "M" & !is.na(studenti$sesso[i])) {
        indice = indice   1
        maschi[indice,] <- studenti[i,]
    }
}

-output

> maschi
  sesso altezza
2     M     182
3     M     176
4     M     193

-Update using the OP's update data

> maschi
  sesso altezza peso scarpe caso matricola mese giorno
2     M     182   75     43    9        -1    5      2
3     M     176   72     45    5        -1    9     29
4     M     193   95     45    6        -1    5      8
5     M     178   68     45    7         6    7     12

data

studenti <- data.frame(sesso = c("F", "M", "M", "M"), altezza = c(168, 182, 176, 193))