Previously I blogged about how to take Python data and turn it back into SPSS data. Here we are going to do the opposite — turn SPSS data into Python objects. First to start out we will make a simple dataset of three variables.
DATA LIST Free /X Y (2F1.0) Z (A1).
BEGIN DATA
1 2 A
4 5 B
7 8 C
END DATA.
DATASET NAME Test.
EXECUTE.To import this data into Python, we need to import the spss class of functions, which then you can read cases from the active dataset using the Cursor attribute. Here is an example of grabbing all of the cases.
*Importing all of the data.
BEGIN PROGRAM Python.
import spss
dataCursor = spss.Cursor()
AllData = dataCursor.fetchall()
dataCursor.close()
print AllData
END PROGRAM.What this then prints out is ((1.0, 2.0, 'A'), (4.0, 5.0, 'B'), (7.0, 8.0, 'C')), a set of nested tuples. You can also just grab one case by replacing dataCursor.fetchall() with dataCursor.fetchone(), in which case it will just return one tuple.
To only grab particular variables from the list, you can pass a set of indices in the spss.Cursor object. Remember, Python indices start at zero, so if you want the first and second variables in the dataset, you need to grab the 0 and 1 indices.
*Only grabbing certain variables.
BEGIN PROGRAM Python.
dataNum = spss.Cursor([0,1])
spNumbers = dataNum.fetchall()
dataNum.close()
print spNumbers
END PROGRAM.This subsequently prints out ((1.0, 2.0), (4.0, 5.0), (7.0, 8.0)). When grabbing one variable, you may want just a list of the objects instead of the nested tuples. Here I use list comprehension to turn the resulting tuples for the Z variable into a nice list.
*Converting to a nice list.
BEGIN PROGRAM Python.
dataAlp = spss.Cursor([2])
spAlp = dataAlp.fetchall()
dataAlp.close()
spAlp_list = [i[0] for i in spAlp] #convert to nice list
print spAlp
print spAlp_list
END PROGRAM.The first print object is (('A',), ('B',), ('C',)), but the second is ['A', 'B', 'C'].
The above code works fine if you know the position of the variable in the file, but if the position can change this won’t work. Here is a one liner to get the variable names of the active dataset and plop them in a list.
*Way to get SPSS variable names.
BEGIN PROGRAM Python.
varList = [spss.GetVariableName(i) for i in range(spss.GetVariableCount())]
print varList
END PROGRAM.Now if you have your list of variable names you want, you can figure out the index value. There are two ways to do it, iterate over the list of variable names in the dataset, or iterate over the list of your specified variables. I do the latter here (note this will result in an error if you supply a variable name not in the dataset).
*Find the indices of specific variables.
BEGIN PROGRAM Python.
LookVars = ["X","Z"]
VarInd = [varList.index(i) for i in LookVars]
print VarInd
END PROGRAM.Now you can just supply VarInd above to the argument for spss.Cursor to grab those variables. Here I wrapped it all up in a function.
*Easy function to use.
BEGIN PROGRAM Python.
import spss
def AllSPSSdat(vars):
if vars == None:
varNums = range(spss.GetVariableCount())
else:
allvars = [spss.GetVariableName(i) for i in range(spss.GetVariableCount())]
varNums = [allvars.index(i) for i in vars]
data = spss.Cursor(varNums)
pydata = data.fetchall()
data.close()
return pydata
END PROGRAM.You can either supply a list of variables or None, in the latter case all of the variables are returned.
BEGIN PROGRAM Python.
MyDat = AllSPSSdat(vars=["Y","Z"])
print MyDat
END PROGRAM.This set of nested tuples is then pretty easy to convert to other Python objects. Panda’s dataframes, Numpy arrays, and NetworkX objects are all one liners. Here is turning the entire dataset into a panda’s data frame.
*Turn into pandas data frame.
BEGIN PROGRAM Python.
import pandas as pd
MyDat = AllSPSSdat(vars=None)
allvars = [spss.GetVariableName(i) for i in range(spss.GetVariableCount())]
PanDat = pd.DataFrame(list(MyDat),columns=allvars)
print PanDat
END PROGRAM.Which prints out.
X Y Z
0 1 2 A
1 4 5 B
2 7 8 C
Andrew Wheeler 