Shortcuts for specifying multiple variables in SPSS - spss

Are there any shortcuts codes in SPSS for listing multiple variables? Say something similar to v1-v3 instead of v1 v2 v3 in SAS data step?

Some commands allow you to use the TO modifier (but not all). This is dependent on variables being in correct order in the data matrix. There are also multiple response sets, and defining macro calls to a specific set of variables.
Below I give examples of using TO and defining a set of variables via a macro. I admittedly never use multiple response sets, so I can only state it is an option (more useful for a set of dichotomous items than continuous variables I believe).
set seed = 10.
input program.
loop #i = 1 to 100.
compute id = #i.
compute V1 = RV.NORM(0,1).
compute V2 = RV.UNIFORM(0,1).
compute V3 = RV.POISSON(3).
compute V4 = RV.BERNOULLI(.5).
compute V5 = RV.BINOM(5,.8).
end case.
end loop.
end file.
end input program.
dataset name sim.
execute.
freq var V1 to V5 /format = notable /statistics = mean.
DEFINE !myvars () V1 V2 V3 V4 V5.
!ENDDEFINE.
set mprint on.
freq var !myvars /format = notable /statistics = mean.

TO is always based on file order. It would be rare IMO to want a list selected by an interval in alphabetical order. Commands that accept a list of variables pretty much all honor TO.
You can change the variable order by using the KEEP subcommand of MATCH FILES.
You can also define a macro for a list of variables and reference it where you need the list.
Finally, if you install the Python Essentials from the SPSS Community website (www.ibm.com/developerworks/spssdevcentral) and the SPSSINC SELECT VARIABLES extension command, the dialog box makes it easy to define a macro based on file order, alpha order or measurement level, among other criteria.
HTH

Related

gretl - dummy interactions

There does not seem to be an "easy" way (such as in R or python) to create interaction terms between dummy variables in gretl ?
Do we really need to code those manually which will be difficult for many levels? Here is a minimal example of manual coding:
open credscore.gdt
SelfemplOwnRent=OwnRent*Selfempl
# model 1
ols Acc 0 OwnRent Selfempl SelfemplOwnRent
Now my manual interaction term will not work for factors with many levels and in fact does not even do the job for binary variables.
Thanks,
ML
One way of doing this is to use lists. Use the dummify-command for generating dummies for each level and the ^-operator for creating the interactions. Example:
open griliches.gdt
discrete med
list X = dummify(med)
list D = dummify(mrt)
list INT = X^D
ols lw 0 X D INT
The command discrete turns your variable into a discrete variable and allows to use dummify (this step is not necessary if your variable is already discrete). Now all interactions terms are stored in the list INT and you can easily assess them in the following ols-command.
#Markus Loecher on your second question:
You can always use the rename command to rename a series. So you would have to loop over all elements in list INT to do so. However, I would rather suggest to rename both input series, in the above example mrt and med respectively, before computing the interaction terms if you want shorter series names.

When are placeholders necessary?

Every TensorFlow example I've seen uses placeholders to feed data into the graph. But my applications work fine without placeholders. According to the documentation, using placeholders is the "best practice", but they seem to make the code unnecessarily complex.
Are there any occasions when placeholders are absolutely necessary?
According to the documentation, using placeholders is the "best practice"
Hold on, this quote is out-of-context and could be misinterpreted. Placeholders are the best practice when feeding data through feed_dict.
Using a placeholder makes the intent clear: this is an input node that needs feeding. Tensorflow even provides a placeholder_with_default that does not need feeding — but again, the intent of such a node is clear. For all purposes, a placeholder_with_default does the same thing as a constant — you can indeed feed the constant to change its value, but is the intent clear, would that not be confusing? I doubt so.
There are other ways to input data than feeding and AFAICS all have their uses.
A placeholder is a promise to provide a value later.
Simple example is to define two placeholders a,b and then an operation on them like below .
a = tf.placeholder(tf.float32)
b = tf.placeholder(tf.float32)
adder_node = a + b # + provides a shortcut for tf.add(a, b)
a,b are not initialized and contains no data Because they were defined as placeholders.
Other approach to do same is to define variables tf.Variable and in this case you have to provide an initial value when you declare it.
like :
tf.global_variables_initializer()
or
tf.initialize_all_variables()
And this solution has two drawbacks
Performance wise that you need to do one extra step with calling
initializer however these variables are updatable .
in some cases you do not know the initial values for these variables
so you have to define it as a placeholder
Conclusion :
use tf.Variable for trainable variables such as weights (W) and biases (B) for your model or when Initial values are required in
general.
tf.placeholder allows you to create operations and build computation graph, without needing the data. In TensorFlow
terminology, we then feed data into the graph through these
placeholders.
I really like Ahmed's answer and I upvoted it, but I would like to provide an alternative explanation that might or might not make things a bit clearer.
One of the significant features of Tensorflow is that its operation graphs are compiled and then executed outside of the original environment used to build them. This allows Tensorflow do all sorts of tricks and optimizations, like distributed, platform independent calculations, graph interoperability, GPU computations etc. But all of this comes at the price of complexity. Since your graph is being executed inside its own VM of some sort, you have to have a special way of feeding data into it from the outside, for example from your python program.
This is where placeholders come in. One way of feeding data into your model is to supply it via a feed dictionary when you execute a graph op. And to indicate where inside the graph this data is supposed to go you use placeholders. This way, as Ahmed said, placeholder is a sort of a promise for data supplied in the future. It is literally a placeholder for things you will supply later. To use an example similar to Ahmed's
# define graph to do matrix muliplication
x = tf.placeholder(tf.float32)
y = tf.placeholder(tf.float32)
# this is the actual operation we want to do,
# but since we want to supply x and y at runtime
# we will use placeholders
model = tf.matmul(x, y)
# now lets supply the data and run the graph
init = tf.global_variables_initializer()
with tf.Session() as session:
session.run(init)
# generate some data for our graph
data_x = np.random.randint(0, 10, size=[5, 5])
data_y = np.random.randint(0, 10, size=[5, 5])
# do the work
result = session.run(model, feed_dict={x: data_x, y: data_y}
There are other ways of supplying data into the graph, but arguably, placeholders and feed_dict is the most comprehensible way and it provides most flexibility.
If you want to avoid placeholders, other ways of supplying data are either loading the whole dataset into constants on graph build or moving the whole process of loading and pre-processing the data into the graph by using input pipelines. You can read up on all of this in the TF documentation.
https://www.tensorflow.org/programmers_guide/reading_data

Delete variables based on the number of observations

I have an SPSS file that contains about 1000 variables and I have to delete the ones having 0 valid values. I can think of a loop with an if statement but I can't find how to write it.
The simplest way would be to use the spssaux2.FindEmptyVars Python function like this:
begin program.
import spssaux2
spssaux2.FindEmptyVars(delete=True)
end program.
If you don't already have the spssaux2 module installed, you would need to get it from the SPSS Community website or the IBM Predictive Analytics site and save it in the python\lib\site-packages directory under your Statistics installation.
Otherwise, the VALIDATEDATA command, if you have it, will identify the variables violating such rules as maximum percentage of missing values, but you would have to turn that output into a DELETE VARIABLES command. You could also look for variables with zero missing values using, say, DESCRIPTIVES and select out the ones with N=0.
If you've never worked with python in SPSS, here's a way to get the job done without it (not as elegant, but should do the job):
This will count the valid cases in each variable, and select only those that have 0 valid cases. Then you'll manually copy the names of these variables into a syntax command that will delete them.
DATASET NAME Orig.
DATASET DECLARE VARLIST.
AGGREGATE /OUTFILE='VARLIST'/BREAK=
/**list_all_the_variable_names_here = NU(*FirstVarName to *LastVarName).
DATASET ACTIVATE VARLIST.
VARSTOCASES /MAKE NumValid FROM *FirstVarName to *LastVarName/INDEX=VarName(NumValid).
SELECT IF NumValid=0.
EXECUTE.
Pause here to copy the remaining names in the list and complete the syntax, then continue:
DATASET ACTIVATE Orig.
DELETE VARIABLES *paste_here_all_the_remaining_variable_names_from_varlist .
Notes:
* I put stars where you have to replace my text with your variable names.
** If the variables are neatly named like Q1, Q2, Q3 .... Q1000, you can use the "FirstVarName to LastVarName" form (Q1 to Q1000) instead of listing all the variable names.
BTW it is of course possible to do this completely automatically without manually copying those names (using only syntax, no Python), but the added complexity is not worth bothering with for a single use...

How do you include categories with 0 responses in SPSS frequency output?

Is there a way to display response options that have 0 responses in SPSS frequency output? The default is for SPSS to omit in the frequency table output any response option that is not selected by at least a single respondent. I looked for a syntax-driven option to no avail. Thank you in advance for any assistance!
It doesn't show because there is no one single case in the data is with that attribute. So, by forcing a row of zero you'll need to realize we're asking SPSS to do something incorrect.
Having said that, you can introduce a fake case with the missing category. E.g. if you have Orange, Apple, and Pear, but no one answered they like Pear, the add one fake case that says Pear.
Now, make a new weight variable that consists of only 1. But for the Pear case, make it very very small like 0.00001. Then, go to Data > Weight Cases > Weight cases by and put that new weight variable over. Click OK to apply. Now what happens is that SPSS will treat the "1" with a weight of 1 and the fake case with a weight that is 1/10000 of a normal case. If you rerun the frequency you should see the one with zero count shows up.
If you have purchased the Custom Table module you can also do that directly as well, as far as I can tell from their technical document. That module costs 637 to 3630 depending on license type, so probably only worth a try if your institute has it.
So, I'm a noob with SPSS, I (shame on me) have a cracked version of SPSS 22 and if I understood your question correctly, this is my solution:
double click the Frequency table in Output
right click table, select Table Properties
go to General and then uncheck the Hide empty rows and columns option
Hope this helps someone!
If your SPSS version has no Custom Tables installed and you haven't collected money for that module yet then use the following (run this syntax):
*Note: please use variable names up to 8 characters long.
set mxloops 1000. /*in case your list of values is longer than 40
matrix.
get vars /vari= V1 V2 /names= names /miss= omit. /*V1 V2 here is your categorical variable(s)
comp vals= {1,2,3,4,5,99}. /*let this be the list of possible values shared by the variables
comp freq= make(ncol(vals),ncol(vars),0).
loop i= 1 to ncol(vals).
comp freq(i,:)= csum(vars=vals(i)).
end loop.
comp names= {'vals',names}.
print {t(vals),freq} /cnames= names /title 'Frequency'. /*here you are - the frequencies
print {t(vals),freq/nrow(vars)*100} /cnames= names /format f8.2 /title 'Percent'. /*and percents
end matrix.
*If variables have missing values, they are deleted listwise. To include missings, use
get vars /vari= V1 V2 /names= names /miss= -999. /*or other value
*To exclude missings individually from each variable, analyze by separate variables.

Getting length of vector in SPSS

I have an sav file with plenty of variables. What I would like to do now is create macros/routines that detect basic properties of a range of item sets, using SPSS syntax.
COMPUTE scale_vars_01 = v_28 TO v_240.
The code above is intended to define a range of items which I would like to observe in further detail. How can I get the number of elements in the "array" scale_vars_01, as an integer?
Thanks for info. (as you see, the SPSS syntax is still kind of strange to me and I am thinking about using Python instead, but that might be too much overhead for my relatively simple purposes).
One way is to use COUNT, such as:
COUNT Total = v_28 TO v_240 (LO THRU HI).
This will count all of the valid values in the vector. This will not work if the vector contains mixed types (e.g. string and numeric) or if the vector has missing values. An inefficient way to get the entire count using DO REPEAT is below:
DO IF $casenum = 1.
COMPUTE Total = 0.
DO REPEAT V = v_28 TO V240.
COMPUTE Total = Total + 1.
END REPEAT.
ELSE.
COMPUTE Total = LAG(Total).
END IF.
This will work for mixed type variables, and will count fields with missing values. (The DO IF would work the same for COUNT, this forces a data pass, but for large datasets and large lists will only evaluate for the first case.)
Python is probably the most efficient way to do this though - and I see no reason not to use it if you are familiar with it.
BEGIN PROGRAM.
import spss
beg = 'X1'
end = 'X10'
MyVars = []
for i in xrange(spss.GetVariableCount()):
x = spss.GetVariableName(i)
MyVars.append(x)
len = MyVars.index(end) - MyVars.index(beg) + 1
print len
END PROGRAM.
Statistics has a built-in macro facility that could be used to define sets of variables, but the Python apis provide much more powerful ways to access and use the metadata. And there is an extension command SPSSINC SELECT VARIABLES that can define macros based on variable metadata such as patterns in names, measurement level, type, and other properties. It generates a macro listing these variables that can then be used in standard syntax.

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