weekBegin

weekBegin(X, [weekday=0], [offset], [n=1])

For each element of X, return the first date of the week that it belongs to and that starts on the day as specified by parameter weekday.

• If parameter weekday>weekday(X, false): for each element of X, return a date that corresponds to the specified weekday parameter in the previous calendar week.

• If parameter weekday<=weekday(X, false): for each element of X, return a date that corresponds to the specified weekday parameter in the same calendar week.

If parameter offset is specified, the result is updated every n weeks. Please refer to example 2 below. The parameters offset and n must be specified together, and offset takes effect only when n > 1.

X is a scalar/vector of type DATE, DATETIME, DATEHOUR, TIMESTAMP or NANOTIMESTAMP.

weekday (optional) is an integer from 0 to 6. 0 means Monday, 1 means Tuesday, ..., and 6 means Sunday. The default value is 0.

offset (optional) is a scalar of the same data type as X. It must be no greater than the minimum value of X. The default value is the minimum value of X.

n (optional) is a positive integer. The default value is 1.

A scalar or vector of the DATE type.

Example 1

t = table(2017.12.01..2017.12.14 as date);
update t set weekday=weekday(date, false), weekBegin=weekBegin(date), weekBegin4=weekBegin(date,4);
t;

Example 2

 t = table(2018.01.03+0..10*3 as date, 0..10 as x);
 update t set weekday=weekday(date, false), weekBegin=weekBegin(date,,2018.01.02,2);
 t;

Example 3

date=2012.10.02 2012.10.03 2012.10.07 2012.10.08 2012.10.12 2012.10.16 2012.10.18 2012.10.20 2012.10.25 2012.10.28
time=[09:34:07,09:36:42,09:36:51,09:36:59,09:32:47,09:35:26,09:34:16,09:34:26,09:38:12,09:38:13]
sym = take(`MSFT,10)
price= 49.6 29.46 29.52 30.02 174.97 175.23 50.76 50.32 51.29 52.38
qty = 2200 1900 2100 3200 6800 5400 1300 2500 8800 4500
t1 = table(date, time, sym, qty, price);

t1;

select avg(price),sum(qty) from t1 group by weekBegin(date, 4, 2012.10.01, 2);

Related function: weekEnd