Chapter 7. Combining data sets

Chapter 7. Combining data sets - 1 Combining data sets 2 ¡...

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Unformatted text preview: 1 Combining data sets 2 ¡ Needs ¡ Stacking ¡ Matching and Merging ¡ Updating 3 Need for combining data ¡ Facts ¢ Powerful statistical analysis methods are built in SAS PROCs ¢ Observation is the fundamental unit of operation in data analysis tasks within SAS PROCs ¡ However, ¢ Data may not be in a single data set ¢ A logical unit of data may not be in a single observation ¡ Therefore, we have to logically relate and combine out data before performing data analysis tasks 4 ¡ A complete collection of data records (observations) are from different sources (data sets) ¢ Data are archived according to year or branch ¢ Many SAS PROCs operate on a single data set ¡ A complete collection of information about a single entity (a complete single observation) are from different sources (observations in a number of data sets) ¢ Information about a patient: (i) medical records, (ii) medical tests result, (iii) hospital visits records, and (iv) demographic record, etc.. ¢ The unit of data analysis tasks in many SAS PROCs is single observation within a single data set 5 Methods for combining SAS data sets ¡ Stacking ¢ Observations from 2 or more data sets are combined into a single data set ¢ Each observation in the combined data set is solely from one of the data set ¢ 2 subtypes ¡ Concatenate – stack data sets sequentially ¡ Interleave – stack observations from data sets, ordered by one or more common variables 6 ¡ Matching ¢ Observations from 2 or more data sets are matched into one observation in the combined data set ¢ The operation uses 2 or more independent SET statements applying to each of the data sets ¢ The matching operation stops when any one of the data sets reaches the end. It is not a complete merging of data sets. In merging, all observations in all data set will be combined in some way to form the resultant data set 7 ¡ Merging ¢ Observations from 2 or more data sets are merged into one observation in the combined data set ¢ 2 subtypes ¡ One-to-one merge – combine observations in data sets into a single observation based on their relative position in the original data sets ¡ Matched-merge – combine observations in data sets according to the values of one or more common variables ¡ Updating – applying changes to a master data set from a transaction data set based upon the values of key variables 8 Concatenation 024 010 004 001 024 009 004 002 janpat febpat Patient # Patient # 024 010 004 001 024 009 004 002 Patient # Combined data set jan2feb data jan2feb; set janpat febdat; run; 9 ¡ Concatenation is to stack data sets – place observations of one data set after another ¡ Concatenation results in a data set that has as many observations as the sum of all the observations in the data sets being combined ¡ There are a number of methods that can be used to concatenate data sets. The most general way is to use a SET statement with multiple data sets ¡ Note: PROC APPEND is another way to concatenate data sets 10...
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This note was uploaded on 02/09/2012 for the course STAT 1301 taught by Professor Smslee during the Spring '08 term at HKU.

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Chapter 7. Combining data sets - 1 Combining data sets 2 ¡...

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