Arrays in SAS are incredibly useful things. For example, if you’re dealing with a concomitant medications dataset and want to check for certain medicines across multiple columns, you’d be hard-pressed to find a faster method than using arrays!<\/p>\n\n\n\n
Within the SDTM.CM domain, medication names are spread across several columns, usually: CMTRT (Reported Name of Drug, Med, or Therapy), CMMODIFY (Modified Reported Name), and CMDECOD (Standardized Medication Name).<\/p>\n\n\n\n
If we wanted to find and flag, for example, the following three medicines: Aspirin, Antacid, Potassium Chloride ; we could do it as follows:<\/p>\n\n\n\n
\ndata cm;\n set sdtm.cm;\n\n array all_meds {*} $ cmtrt cmmodify cmdecod;\n array check_meds {3} $ _temporary_ (\"aspirin\", \"antacid\", \"potassium chloride\");\n\n do i = 1 to dim(all_meds);\n do j = 1 to dim(check_meds);\n if upcase(all_meds[i]) = upcase(check_meds[j]) then occur = \"Y\";\n end;\n end;\n\n if occur ^= \"Y\" then delete;\nrun;\n<\/code><\/pre>\n\n\n\nThe above method works well to quickly check for multiple conmeds across multiple columns. However, usually a conmeds list is not restricted to only 3 items and counting the number of unique items is a slow and tedious process. If an item needs to be added or removed, then the space to be reserved needs to be updated.<\/p>\n\n\n\n
Unfortunately specifying the list of conmeds in a temporary array prevents the use of the dynamic sizing, usually indicated by {*}. This is something that will hopefully be fixed in a newer version of SAS, but until such time I’ve taken it upon myself to create a macro which creates dynamically sized (sort of!) temporary arrays. It does this by counting the number of items and automatically reserving the space for it.<\/p>\n\n\n\n
Note:<\/strong> if you are feeling lazy, you can still create a temporary array and simply oversize it, e.g., specify a size of 100 items even though you may only need half that. However, this will result in SAS posting a WARNING to the log about partial array initialization, which is not ideal in the pharmaceutical environment where we want clean logs! <\/p>\n\n\n\nIf you’d prefer to avoid another O(n) loop which checks for the maximum length needed for character variables, simply set a static length, say $20.<\/p>\n\n\n\n
\n\/*\n Macro makeTempArray\n \n Purpose: To create temporary arrays without knowing the\n size of the array needed beforehand. This is a \n limitation of the original SAS procedure for\n creating temporary arrays.\n \n Parameters:\n arrayname : an arbitrary name for your array\n ischar : pass either Y for a character array \n or N for numeric\n items : pass the list of items to be contained in\n the array, wrapped in %str() and separated\n by commas\n*\/\n\n%macro makeTempArray(arrayname=, ischar=, items=);\n %let n=%sysfunc(countw(&items., %str(,), )); \/*count the number of items to reserve space for*\/\n \n %if &ischar.=Y %then %do; \/*if this is a character array, we need the length of the longest item*\/ \n %let l = 1;\n %do j = 1 %to &n.;\n %let l0 = %sysfunc(length(%sysfunc(scan(&items., &j., %str(,), r))));\n %if &l0. > &l. %then %let l = &l0.;\n %end;\n %end;\n \n array &arrayname. {&n.} %if &ischar.=Y %then $&l.; _temporary_ (\n %do i = 1 %to &n.;\n %let item = %sysfunc(scan(&items., &i., %str(,), r));\n %if &ischar.=Y %then %str(\"&item.\" ); %else &item.;\n %end;\n );\n%mend makeTempArray;\n<\/code><\/pre>\n\n\n\nWith this macro, we can now modify our initial starting block of code as follows (items must be separated by commas):<\/p>\n\n\n\n
\ndata cm;\n set sdtm.cm;\n\n array all_meds {*} $ cmtrt cmmodify cmdecod;\n %makeTempArray(arrayname=%str(check_meds), ischar=%str(Y), items=%str(aspirin, antacid, potassium chloride));\n\n do i = 1 to dim(all_meds);\n do j = 1 to dim(check_meds);\n if upcase(all_meds[i]) = upcase(check_meds[j]) then occur = \"Y\";\n end;\n\n if occur = \"Y\" then leave;\n end;\n\n if occur ^= \"Y\" then delete;\nrun;\n<\/code><\/pre>\n\n\n\nHope this helps you next time you need to cross-check multiple items across multiple columns! Happy hacking!<\/p>\n\n\n\n
Updates:<\/strong> My colleague, Mazi Ntintelo has rightly pointed out that the commas within the macro’s scan functions should be wrapped as %str(,)<\/em> and also that the do<\/em> loop checking for conmeds can be optimised with a leave<\/em> statement. Thanks, Mazi!<\/p>\n","protected":false},"excerpt":{"rendered":"Arrays in SAS are incredibly useful things. For example, if you’re dealing with a concomitant medications dataset and want to check for certain medicines across multiple columns, you’d be hard-pressed to find a faster method than using arrays! Within the SDTM.CM domain, medication names are spread across several columns, usually: CMTRT (Reported Name of Drug, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2,67,53,54],"tags":[126,128,130,131,129,55,127],"class_list":["post-490","post","type-post","status-publish","format-standard","hentry","category-computer-science","category-pharma","category-programming","category-sas","tag-arrays","tag-character","tag-dynamic-size","tag-macro","tag-numeric","tag-sas","tag-temporary"],"_links":{"self":[{"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=\/wp\/v2\/posts\/490","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=490"}],"version-history":[{"count":15,"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=\/wp\/v2\/posts\/490\/revisions"}],"predecessor-version":[{"id":505,"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=\/wp\/v2\/posts\/490\/revisions\/505"}],"wp:attachment":[{"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=490"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=490"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/jvdl.me\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=490"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}