[求助]请大家帮忙看下这题,3xxxxx

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这两题得区别在哪呀?

1.A raw data file is listed below:
RANCH,1250,2,1,Sheppard Avenue,"$64,000"
SPLIT,1190,1,1,Rand Street,"$65,850"
CONDO,1400,2,1.5,Market Street,"80,050"
TWOSTORY,1810,4,3,Garris Street,"$107,250"
RANCH,1500,3,3,Kemble Avenue,"$86,650"
SPLIT,1615,4,3,West Drive,"94,450"
SPLIT,1305,3,1.5,Graham Avenue,"$73,650"
The following SAS program is submitted using the raw data file as input:
data work.condo_ranch;
infile'file-specification' dsd;
input style $ @;
if style = 'CONDO' or style = 'RANCH' then
input sqfeet bedrooms baths street $ price : dollar10.;
run;
How many observations does the WORK.CONDO_RANCH data set contain?
A. 0
B. 3
C. 5
D. 7
Answer: D

2.QUESTION 14
A raw data file is listed below:
RANCH,1250,2,1,Sheppard Avenue,"$64,000"
SPLIT,1190,1,1,Rand Street,"$65,850"
CONDO,1400,2,1.5,Market Street,"80,050"
TWOSTORY,1810,4,3,Garris Street,"$107,250"
RANCH,1500,3,3,Kemble Avenue,"$86,650"
SPLIT,1615,4,3,West Drive,"94,450"
SPLIT,1305,3,1.5,Graham Avenue,"$73,650"
The following SAS program is submitted using the raw data file as input:
data work.condo_ranch;infile'file-specification' dsd;
input style $ @;
if style = 'CONDO' or style = 'RANCH';
input sqfeet bedrooms baths street $ price : dollar10.;
run;
How many observations will the output data set contain?
A. 0
B. 3
C. 5
D. 7
Answer: B

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关键词：observations observation following observat Specific 帮忙

第一题的倒数第三行是“if style = 'CONDO' or style = 'RANCH' then”，在第二题的同样位置则是“if style = 'CONDO' or style = 'RANCH';”

第一题if...then的选择作用体现在变量（Var）的读入过程中，即style的差异将影响input的对象。但是不论读取了哪些变量，该命令对每个变量下观测值的个数是没有影响的。

第二题的if则是求子集的语句，效果是只有符合条件的观测（Obs）才能进入的当前数据集。与第一题相反，对变量倒是没有选择的。

两道题目问的都是“How many observations...”，因此第一题是有7个，而第二题有3个（RANCH,1250,...、CONDO,1400,...和RANCH,1500,...）

我是这样理解的，不知是否说得通。

wonderful explanation!

However, row is obs.,column is var.

第一题得结果如果是 RANCH,1250,2,1,Sheppard Avenue,$64,000, 应该是7个obs

但是第二题如何解释只有3个obs???

[此贴子已经被作者于2007-3-12 6:35:32编辑过]

如果数据是“RANCH,1250,2,1,Sheppard Avenue,$64,000”，那么应该是有7个Var，因为有7列（column）。这对每一行的观测而言只是多出一个信息，但对于总共的行数（也就是观测个数）是没有影响的。