Data Manipulation with LAG Functions

This program starts by creating a 't1' dataset with hardcoded values. It then sorts this data by the 'x' variable. A subsequent Data Step ('t2') uses the LAG function to create a new variable 'z' containing the previous value of 'y'. Finally, a last step ('t3') applies complex conditional logic using comparisons between current and lagged values to modify variables.

Data Analysis

Type : CREATION_INTERNE

Data is created directly in the code via the CARDS statement in the data t1 step.

1 Code Block

DATA STEP Data

Explanation :
Creation of table 't1' with two numeric variables x and y, populated by internal data (CARDS).

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1	DATA t1;
2	INPUT x y;
3	CARDS;
4	1 5
5	2 6
6	3 6
7	7 9
8	8 10
9	11 12
10	;
11	RUN;

2 Code Block

PROC SORT

Explanation :
Sorting table 't1' in ascending order by variable 'x'.

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1	PROC SORT DATA=t1; BY x; RUN;

3 Code Block

DATA STEP Data

Explanation :
Creation of table 't2' from 't1'. The LAG(y) function is used to retrieve the value of 'y' from the previous observation and store it in 'z'.

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1	DATA t2;
2	SET t1 END=b;
3	z=lag(y);
4	/*if x>z or b;
5	proc sort; by decending x;
6	*/
7	RUN;

4 Code Block

PROC PRINT

Explanation :
Displaying the content of the last created table (t2) in the standard output.

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1	PROC PRINT;RUN;

5 Code Block

DATA STEP Data

Explanation :
Creation of table 't3' from 't2'. Applies conditional modifications: if x is less than z, z takes the value of y. Then, y is updated with the maximum between its current value and the previous value of z.

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1	DATA t3;
2	SET t2;
3	IF xTHEN z=y;
4	y=max(y,lag(z));
5	*if y^=z;
6	RUN;

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