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Analyzing and Presenting Your Data by Week: The Essential Guide to Using the WEEK Function in Looker Studio

The WEEK function in Google Data Studio is an excellent tool for analyzing and presenting data according to weekly cycles. It allows users to efficiently break down a date parameter on the basis of weeks to better measure and compare growth, performance, sales and other metrics.

Isolating the week can provide invaluable insights in trends that may not be apparent in daily or monthly data. For instance, it could help uncover patterns in a retail setting whereby certain products do better in specific weeks of the year.

Syntax of the WEEK Function:

With two primary ways to use the WEEK function, users have flexibility based on data type: semantic date field or compatibility mode date.

Semantic date field:
```
WEEK(date_expression)
```
Compatibility mode date:
```
WEEK(X [, Input Format])
```

Where: -

date_expression

is a Date & Time field or expression. -

is a field or expression that evaluates to Text, Number, or compatibility mode Date. - Input Format is optional if

is correctly configured as a semantic date field but mandatory for compatibility mode dates.

How the WEEK Function works:

The WEEK function's primary role is returning the week number for a given date.

In the case of a semantic date field, you only need to input

date_expression

into

WEEK(date_expression)

in the syntax.

On the other hand, for a compatibility mode Date value, the syntax

WEEK(X [, Input Format])

requires the additional 'Input Format' definition if

isn't already set as a semantic date field.

Examples of the WEEK Function:

Consider an electronics store that wants to analyze its weekly sales data. The store records the sales date for each transaction. They could use the WEEK function like so:

With semantic date field:
```
WEEK(Sales_Date)
```
If Sales_Date == '2019-01-01', the output will be '1'
With compatibility mode date:
```
WEEK(Sales_Date, 'DEFAULT_DASH')
```
If Sales_Date == '2019/01/01-09:40:45', the output will be '1'

These examples demonstrate how the WEEK function can be used to identify the week of the year a sale was made, helping to group sales data for weekly performance analysis.

Limitations of the WEEK Function:

While useful, the WEEK function has its constraints. It operates per the ISO 8601 standard, which may differ from local calendar's week number, especially for dates close to the start and end of the year.

Also, the function won't directly associate data with day of the week (Monday, Tuesday, etc.), which is sometimes a more useful metric when analyzing trends and patterns.

Tips for the WEEK Function:

If not sure about the format of date data, confirm whether your date fields are semantic dates or compatibility mode dates to use the correct syntax.
To better analyze data, consider creating a custom field to break down data by week and day using functions like WEEK and DAY.
When working with compatibility mode date values, remember to define 'Input Format' to prevent errors and ensure accurate week identification.

With the power to dissect data week by week, you are better equipped to track patterns and make data-informed decisions for improved business performance.

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