GATHER

GATHER (LET)

Let Subcommand

Extract rows of a variable based on index values contained in another variable.

It is sometimes convenient to extract specific rows of a variable. Although this can usually be accomplished using SUBSET/EXCEPT/FOR clauses, the GATHER command can sometimes be more convenient. This is particularly true if the desired rows do not follow a regular pattern. Also, if you are going to perform an extensive set of operations on the subset of the data, it may be more convenient to use the GATHER command than to use the SUBSET command on many subsequent commands.

With the GATHER command, we define a separate variable that contains the specific rows we want to extract.

If you modify the extracted data and want to save these modified values back to the original variable, you can use the SCATTER command. Enter HELP SCATTER for further information.

LET <y> = GATHER <x> <index>
where <x> is a response variable;
            <index> is a variable containing row numbers;
            and <y> is a variable (of length equal to <index>) that contains the rows of <x> corresponding to <index>.

LET Y = GATHER X INDEX

None

None

SCATTER	= Save data from a variable to specified rows of another variable based on an index variable.
SEQUENCE	= Generate a patterned sequence of values.
SORT	= Sort a column of numbers.
RANK	= Rank a column of numbers.
CODE	= Code a column of numbers.
SUBSET	= Specifies a subset to be included in a plot, analysis, or LET command.
RETAIN	= Retain specified rows or a subset of a variable.

Data Transformation

2008/11

 
let n = 30
let xseq = sequence 1 1 n
let x = normal rand numb for i = 1 1 n
let iindex = data 10  14  8  23  19
.
let y = gather x iindex
set write decimals 3
print xseq x iindex y
    

The following output is generated.

          1.000         -1.073         10.000          0.270
          2.000          0.573         14.000         -0.841
          3.000         -0.873          8.000          0.032
          4.000          0.234         23.000         -1.063
          5.000         -0.455         19.000          0.034
          6.000         -0.525          0.000          0.000
          7.000         -0.706          0.000          0.000
          8.000          0.032          0.000          0.000
          9.000          1.191          0.000          0.000
         10.000          0.270          0.000          0.000
         11.000         -0.149          0.000          0.000
         12.000         -0.197          0.000          0.000
         13.000         -0.243          0.000          0.000
         14.000         -0.841          0.000          0.000
         15.000         -0.104          0.000          0.000
         16.000          0.419          0.000          0.000
         17.000          0.264          0.000          0.000
         18.000          0.898          0.000          0.000
         19.000          0.034          0.000          0.000
         20.000          1.588          0.000          0.000
         21.000          0.389          0.000          0.000
         22.000         -0.470          0.000          0.000
         23.000         -1.063          0.000          0.000
         24.000         -0.027          0.000          0.000
         25.000         -0.464          0.000          0.000
         26.000          0.592          0.000          0.000
         27.000         -0.506          0.000          0.000
         28.000         -0.360          0.000          0.000
         29.000          0.499          0.000          0.000
         30.000          0.243          0.000          0.000