# Analysis in R: Iteration and conditional decision commands

The R operation combines commands to process data and output results. In many cases there is rarely a single element in the data, but rather several elements, and each element is processed repeatedly and the results are output. Therefore, repetition and conditional evaluation commands are introduced here.

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## Repeat the command: for ( element in the number of processes ) {process}

The “for” command repeats the number of times the element (often set to a single letter, such as i, m, etc. in alphabetical order) inside the parentheses will be processed. For example, here is a code that outputs a sequence of numbers from 1 to 7, adding 3 to each.

```data <- c(1, 2, 3, 4, 5, 6, 7)

for (i in seq(data)) {
cat(i + 3, "\n")
}

#Result
4
5
6
7
8
9
10
```

Note that the “in” is followed by “seq(data)” to get the repeated range. “1:7” is also acceptable, but specifying the range by the length of the data to be processed rather than by a number will reduce errors.

## Command for conditional judgment: if (condition) {process 1} else {process 2}

The “if else” command executes process 1 if the condition is true and process 2 if it is not. For example, here is code that outputs a sequence of numbers from 1 to 7, adding 3 only to even numbers.

```data <- c(1, 2, 3, 4, 5, 6, 7)

for(i in seq(data)){

if (i%%2 == 0){

cat(i + 3, "\n")

}else{

#If odd, do not process. Blank

}

}

#Result
5
7
9
```

It can also be processed simply as ifelse(condition, process 1, process 2). However, since NA is included in the result, some processing ingenuity is required.

```ifelse(data%%2 == 0, data + 3, NA)

#Result
 NA 5 NA 7 NA 9 NA
```

I hope this makes your analysis a little easier !!

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