let’s be friends with arrays presentation.pdf · arrays. vibhavari inamdar. any views or opinions...

Let’s be friends with Arrays

Vibhavari Inamdar

Any views or opinions presented in this presentation are solely those of the author and do not necessarily represent those of the company.

www.cytel.com ©2012 Cytel 2

Basic concepts of Array:

What is array Syntax of array Temporary Array Multidimensional arrays

Illustrating the usage of arrays in different scenarios from clinical programming

Agenda


A means for repetitively processing variables .

A convenient way of grouping variables.

Wonderful tool which can be used to refer repetitive values.

What is Array?


Syntax of an array statement

array array-name { n } [ $ ] [ length ] variable-names



array

array-name{ n } [ $ ] [ length ] variable-names

A valid SAS name



array array-name

{ n }

[ $ ] [ length ] variable-names

Dimension of the array



array array-name { n }

[ $ ]

[ length ] variable-names

Character element



array array-name { n } [ $ ]

[ length ]

variable-names

Assign lengths to character variables



array array-name { n } [ $ ] [ length ]

variable-names

Names of the variables :Array elements


Temporary Array :

•Arrays which are required only for calculations and not required in the output dataset.

•The elements are defined by the keyword _TEMPORARY_.

Temporary Array & Multidimensional Arrays

Multidimensional Arrays :•Used when the processing of data depends on more than one factor.

•Created in two or more dimensions.


Illustrating the usage of arrays in different scenarios from in clinical programming


Example 1:Creating Race variableData:


Assign length for new variable “Race”

Read SAS dataset

Define Array

Do Loop

Example 1:Creating Race variable



Read SAS dataset

Define Array

Do Loop

Data dm_race(keep=usubjid Race);

length Race $56;




Read SAS dataset

Define Array

Do Loop

data dm3(keep=usubjid Race);

length Race $56;

set dm2;




Read SAS dataset

Define Array

Do Loop

array RACE_label1(*)$ BLACK ASIAN CAUSASIAN;




Read SAS dataset

Define Array

Do Loop

do i =1 to dim(RACE_label1);

if RACE_label1(i) ne '' then

Call label(RACE_label1(i),Race);

end;

CALL LABEL :

Extracts label of array element and puts in variable “Race”



Assign length for newvariable “Race”

Define array with Racevariables as array elements

Do Loop

Use Call_Label and assign the label of array element in variable “Race”

Recap of example 1:



Output:

Input Data:



Example2:Calculating percentages in the table

Data:


Table:



Number of subjects in each treatment:

Frequencies:


Use proc sql and create macro variables “n1”, “n2”,”n3” with number of subjects under each treatment.


Read SAS dataset

Define Array

Do Loop

data final2

(keep = gender _1D0 _2D0 _0D3 per1

per2 per3 );

set gen;



Read SAS dataset

Define Array

Do Loop

array no{3}_temporary_ (&n1.,&n2. , &n3.);

array freq{3} _1D0 _2D0 _0D3 ;

array percent{3}percent1 percent2 percent3;

array per{3}$ 18 per1 per2 per3;

Creating temporary array for number of subjects in each treatment



Read SAS dataset

Define Array

Do Loop





Array for frequencies



Read SAS dataset

Define Array

Do Loop





Array for percentages



Read SAS dataset

Define Array

Do Loop





Array for concatenation of frequencies and percentages



Read SAS dataset

Define Array

Do Loop

do i=1 to 3;

if freq{i} eq . then freq{i} =0;

percent{i}=(freq{i}/no{i})*100;

per{i}=

compress(put(freq{i},5.0))||''||'('||

compress(put(Percent{i},5.2) )|| ')';

end;

Replacing blanks with Zero



Read SAS dataset

Define Array

Do Loop

do i=1 to 3;



per{i}=



end;

Calculating percentages



Read SAS dataset

Define Array

Do Loop

do i=1 to 3;



per{i}=



end;

Concatenating the frequencies andpercentages


Recap of example 2:

www.cytel.com


Define array

Replacing blanks with Zero

Calculating the percentages

Concatenating the frequencies and percentages

©2012 Cytel 31


Example3:Imputing dates by adding 6 months

Data: Missing date


Transposing the data:



Read SAS dataset

Define Array

Do Loop

data ex3;set _ex2;by usubjid;



Read SAS dataset

Define Array

Do Loop

array st(7) ms: ;



Read SAS dataset

Define Array

Do Loop

do i=1 to 7;if i gt 1 and st(i)=. and st(i-1) ne .

then do;

If the date is missing but theprevious date is not missing



Read SAS dataset

Define Array

Do Loop

st(i)=intnx('month',st(i-1),6);

dd=day(st(i-1));

mm=month(st(i));

yy=year(st(i));

intnx function returns date value

incremented by a specified number of intervals .



Read SAS dataset

Define Array

Do Loop

if dd lt 29 then st(i)=mdy(mm,dd,yy);

else if dd ge 29 and mm=2 then do;

if mod(yy,4)=0 then st(i)=mdy(mm,29,yy);

else st(i)=mdy(mm,28,yy);

end;

While calculating new date,consider if the month is Feb based on date

less than or equal to 29



Read SAS dataset

Define Array

Do Loop

if dd lt 29 then st(i)=mdy(mm,dd,yy);

else if dd ge 29 and mm=2 then do;

if mod(yy,4)=0 then st(i)=mdy(mm,29,yy);

else st(i)=mdy(mm,28,yy);

end;

Consider the Leap year to assign date 29.



Read SAS dataset

Define Array

Do Loop

else if dd ge 29 and mm ne 2 then do;

if dd in (29,30) thenst(i)=mdy(mm,dd,yy);

else if dd=31 then do;

if mm in (1,3,5,7,8,10,12) thenst(i)=mdy(mm,dd,yy);

else if mm in (4,6,9,11) thenst(i)=mdy(mm,30,yy);

If month is not Feb andif date is 31 then check the month of new date.


Recap of example 3:

www.cytel.com

Define array

If date is missingand the previous date is not missing

Intnx function and get new date

Checks on new date


©2012 Cytel 41


Output:

Imputed Dates!!



Input Data:

Example 4:To find the consecutive same result



Transposing the data:


Task:

If the baseline is “positive”

If result is “Negative” for consecutive visits.

At which visit the result turn tobe Negative



Read dataset and check if Baseline is positive

Define Array

Do Loop

data conc;

set ts;

if ag1='Positive' then do;

flag1=1;

end;

.Read the SAS

dataset



Define Array

Do Loop

data conc;

set ts;


flag1=1;

end;



If Baseline is positivethen flag1=1


Define Array

Do Loop

array b(2:5) $ ag2-ag5;




Define Array

Do Loop

do i=2 to 4;

if b(i)="Negative" and b(i+1)="Negative"

then do;

visit=i ;

flag2=1;

i=i+4;

end;

end;

If the consecutive visits have result “Negative”




Define Array

Do Loop

do i=2 to 4;


then do;

visit=i ;

flag2=1;

i=i+4;

end;

end;

Visit at which the result is consecutively

Negative




Define Array

Do Loop

do i=2 to 4;


then do;

visit=i ;

flag2=1;

i=i+4;

end;

end;



If consecutive visits are “negative” then flag2=1


Define Array

Do Loop

do i=2 to 4;


then do;

visit=i ;

flag2=1;

i=i+4;

end;

end;

End the loop if consecutive visits have Negative value.




data conc;

set ts;


flag1=1;

end;

array b(2:5) $ ag2-ag5;

do i=2 to 4;

if b(i)="Negative" and b(i+1)="Negative" then do;

visit=i ;

flag2=1;

i=i+4;

end;

end;

if flag1=1 and flag2>1 then censor=0;

else censor=1;

If baseline is positive and consecutive visits are Negative.


Recap of example 4:

www.cytel.com

Check if baseline is “positive”

Define array

Check if consecutive visits have result

“Negative”

visit where the result turn to be Negative and censor variable


©2012 Cytel54


Some more examples where ARRAY would be of great help

• Calculation of AE Phase

Different periods of the study

Start date and end date of different date

Define array

Calculate AE phase

• Deriving Cycle Variable

Dosing period and Rest Period of each cycle.

Start date of each cycle.

Define array

To calculate End date of cycle.

• And Many more….


Limitations

1. Variables should be either all numeric or character.

2. The dimensions must be supplied at compile time by either hardcoding or macro variables.

3. Array takes longer duration during compiling.

Advantages

1. Array can be used to perform same operation over a set of variables more efficiently.

2. Array can be used to create new variables.

3. Array helps to reduce code length.

4. Program becomes more efficient and saves your time and energy.



Conclusion

•Arrays give us lot of flexibility to manipulate data in different

ways.

•Hope we have raised the toast of friendship towards Arrays and

will consider arrays as convenient approach of programming!!


Questions?


Thank [email protected]

let’s be friends with arrays presentation.pdf · arrays. vibhavari inamdar. any views or opinions...

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