How to make loops in R

There is no reason to use for or other cycles. R is a vectorized programming language, which means it can process entire vectors at once. Here it goes.

First I'm going to transform the column data into an object of class Date . It will not be used but I think it is a step that can be useful in other situations and therefore it does not hurt to do so already.

dados$data <- as.Date(dados$data, "%d/%m/%Y")

Next, create the column with 0 , 1 or 3 .

dif <- c(0, diff(dados$tem_1min))
dados$nota <- as.integer(abs(dif) < 2 | abs(dif) > 3)
dados$nota[is.na(dados$nota)] <- 3L

head(dados, 10)
#   dia   hora       data tem_1min nota
#1    1 1.0000 2012-01-01   20.463    1
#2    1 1.0417 2012-01-01   20.071    1
#3    1 1.0833 2012-01-01   19.462    1
#4    1 1.1250 2012-01-01   19.400    1
#5    1 1.1667 2012-01-01   18.528    1
#6    1 1.2083 2012-01-01   18.428    1
#7    1 1.2500 2012-01-01   18.411    1
#8    1 1.2917 2012-01-01   19.087    1
#9    1 1.3333 2012-01-01   20.063    1
#10   1 1.3750 2012-01-01   21.393    1

Editing.

In comment the following has now been requested.

On each line, assign the value 5 when tem_1min is between 0 and 40 , 6 if outside this range and 7 if there is no data.

inx <- 0 <= dados$tem_1min & dados$tem_1min <= 40
dados$nota2 <- 7L
dados$nota2[inx] <- 5L
dados$nota2[!inx] <- 6L

If I understood your question well, this should help.

For:

for(i in conjunto_de_valores){
  # comandos que 
  # serão repetidos
}

While:

while (condição){
     # comandos a serem repetidos
}

Repeat:

repeat {
    # Comandos a serem repetidos
    # if (Condição para que a repetição pare) break()
}