how to pivot an awk array?

Pivoting data using `awk` involves rearranging data stored in an associative array (also known as a dictionary or hash table in other programming languages) to present it in a different format. The concept of "pivoting" is commonly used when dealing with tabular data where you want to transform rows into columns or vice versa.

Let's assume you have input data in a specific format and you want to pivot it. Here’s a simple example to illustrate how you would do this with `awk`.

### Example Input Data

Consider the following CSV-like input data representing sales data:

```
product,sale,store
A,100,X
A,150,Y
B,200,X
B,300,Y
```

### Expected Output (Pivoted)

For pivoting this input based on products and stores, you might want to see the total sales of each product in each store, like this:

```
product,X,Y
A,100,150
B,200,300
```

### AWK Script to Pivot Data

Here’s a sample `awk` script that can achieve this:

```bash
awk -F, '
NR==1 { 
    # Store the header
    for (i=2; i<=NF; i++) {
        headers[i-1] = $i; 
    }
    next; 
}
{
    # Store sales data in a nested array
    product = $1;
    store = $2;
    sales[product][store] = $3;
    products[product];
    stores[store];
}
END {
    # Print header
    printf "product";
    for (s in stores) {
        printf ",%s", s; 
    }
    print "";

    # Print the pivoted data
    for (p in products) {
        printf "%s", p;
        for (s in stores) {
            printf ",%d", sales[p][s] ? sales[p][s] : 0;
        }
        print "";
    }
}' input.csv
```

### Explanation of the Script

1. **Set the Field Separator**: `-F,` sets the field separator to a comma, which is useful for CSV files.

2. **Header Handling**: In the first `NR==1` block, we read the headers and store them for later use.

3. **Data Storing**: For each subsequent line, we extract the `product`, `store`, and `sale` values, storing the sales in a nested associative array `sales[product][store]` and keeping track of unique products and stores.

4. **Printing the Output**:
   - In the `END` block, we first print the header row.
   - Then we iterate over each product and for each product, iterate over the stores, printing the sales or `0` if there was no sale for that combination.

### Running the Script

To run the above script, save it as `pivot.awk` and execute it:

```bash
awk -f pivot.awk input.csv
```

### Conclusion

This method allows you to pivot an array in `awk` to rearrange your data as needed. Adjust the script according to the specific structure of your input data and the format you want in your output.