|
| 1 | +.. _compare_with_spss: |
| 2 | + |
| 3 | +{{ header }} |
| 4 | + |
| 5 | +Comparison with SPSS |
| 6 | +******************** |
| 7 | +For potential users coming from `SPSS <https://www.ibm.com/spss>`__, this page is meant to demonstrate |
| 8 | +how various SPSS operations would be performed using pandas. |
| 9 | + |
| 10 | +.. include:: includes/introduction.rst |
| 11 | + |
| 12 | +Data structures |
| 13 | +--------------- |
| 14 | + |
| 15 | +General terminology translation |
| 16 | +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 17 | + |
| 18 | +.. csv-table:: |
| 19 | + :header: "pandas", "SPSS" |
| 20 | + :widths: 20, 20 |
| 21 | + |
| 22 | + :class:`DataFrame`, data file |
| 23 | + column, variable |
| 24 | + row, case |
| 25 | + groupby, split file |
| 26 | + :class:`NaN`, system-missing |
| 27 | + |
| 28 | +:class:`DataFrame` |
| 29 | +~~~~~~~~~~~~~~~~~~ |
| 30 | + |
| 31 | +A :class:`DataFrame` in pandas is analogous to an SPSS data file - a two-dimensional |
| 32 | +data source with labeled columns that can be of different types. As will be shown in this |
| 33 | +document, almost any operation that can be performed in SPSS can also be accomplished in pandas. |
| 34 | + |
| 35 | +:class:`Series` |
| 36 | +~~~~~~~~~~~~~~~ |
| 37 | + |
| 38 | +A :class:`Series` is the data structure that represents one column of a :class:`DataFrame`. SPSS doesn't have a |
| 39 | +separate data structure for a single variable, but in general, working with a :class:`Series` is analogous |
| 40 | +to working with a variable in SPSS. |
| 41 | + |
| 42 | +:class:`Index` |
| 43 | +~~~~~~~~~~~~~~ |
| 44 | + |
| 45 | +Every :class:`DataFrame` and :class:`Series` has an :class:`Index` -- labels on the *rows* of the data. SPSS does not |
| 46 | +have an exact analogue, as cases are simply numbered sequentially from 1. In pandas, if no index is |
| 47 | +specified, a :class:`RangeIndex` is used by default (first row = 0, second row = 1, and so on). |
| 48 | + |
| 49 | +While using a labeled :class:`Index` or :class:`MultiIndex` can enable sophisticated analyses and is ultimately an |
| 50 | +important part of pandas to understand, for this comparison we will essentially ignore the :class:`Index` and |
| 51 | +just treat the :class:`DataFrame` as a collection of columns. Please see the :ref:`indexing documentation<indexing>` |
| 52 | +for much more on how to use an :class:`Index` effectively. |
| 53 | + |
| 54 | + |
| 55 | +Copies vs. in place operations |
| 56 | +------------------------------ |
| 57 | + |
| 58 | +.. include:: includes/copies.rst |
| 59 | + |
| 60 | + |
| 61 | +Data input / output |
| 62 | +------------------- |
| 63 | + |
| 64 | +Reading external data |
| 65 | +~~~~~~~~~~~~~~~~~~~~~ |
| 66 | + |
| 67 | +Like SPSS, pandas provides utilities for reading in data from many formats. The ``tips`` dataset, found within |
| 68 | +the pandas tests (`csv <https://raw.githubusercontent.com/pandas-dev/pandas/main/pandas/tests/io/data/csv/tips.csv>`_) |
| 69 | +will be used in many of the following examples. |
| 70 | + |
| 71 | +In SPSS, you would use File > Open > Data to import a CSV file: |
| 72 | + |
| 73 | +.. code-block:: text |
| 74 | +
|
| 75 | + FILE > OPEN > DATA |
| 76 | + /TYPE=CSV |
| 77 | + /FILE='tips.csv' |
| 78 | + /DELIMITERS="," |
| 79 | + /FIRSTCASE=2 |
| 80 | + /VARIABLES=col1 col2 col3. |
| 81 | +
|
| 82 | +The pandas equivalent would use :func:`read_csv`: |
| 83 | + |
| 84 | +.. code-block:: python |
| 85 | +
|
| 86 | + url = ( |
| 87 | + "https://raw.githubusercontent.com/pandas-dev" |
| 88 | + "/pandas/main/pandas/tests/io/data/csv/tips.csv" |
| 89 | + ) |
| 90 | + tips = pd.read_csv(url) |
| 91 | + tips |
| 92 | +
|
| 93 | +Like SPSS's data import wizard, ``read_csv`` can take a number of parameters to specify how the data should be parsed. |
| 94 | +For example, if the data was instead tab delimited, and did not have column names, the pandas command would be: |
| 95 | + |
| 96 | +.. code-block:: python |
| 97 | +
|
| 98 | + tips = pd.read_csv("tips.csv", sep="\t", header=None) |
| 99 | +
|
| 100 | + # alternatively, read_table is an alias to read_csv with tab delimiter |
| 101 | + tips = pd.read_table("tips.csv", header=None) |
| 102 | +
|
| 103 | +
|
| 104 | +Data operations |
| 105 | +--------------- |
| 106 | + |
| 107 | +Filtering |
| 108 | +~~~~~~~~~ |
| 109 | + |
| 110 | +In SPSS, filtering is done through Data > Select Cases: |
| 111 | + |
| 112 | +.. code-block:: text |
| 113 | +
|
| 114 | + SELECT IF (total_bill > 10). |
| 115 | + EXECUTE. |
| 116 | +
|
| 117 | +In pandas, boolean indexing can be used: |
| 118 | + |
| 119 | +.. code-block:: python |
| 120 | +
|
| 121 | + tips[tips["total_bill"] > 10] |
| 122 | +
|
| 123 | +
|
| 124 | +Sorting |
| 125 | +~~~~~~~ |
| 126 | + |
| 127 | +In SPSS, sorting is done through Data > Sort Cases: |
| 128 | + |
| 129 | +.. code-block:: text |
| 130 | +
|
| 131 | + SORT CASES BY sex total_bill. |
| 132 | + EXECUTE. |
| 133 | +
|
| 134 | +In pandas, this would be written as: |
| 135 | + |
| 136 | +.. code-block:: python |
| 137 | +
|
| 138 | + tips.sort_values(["sex", "total_bill"]) |
| 139 | +
|
| 140 | +
|
| 141 | +String processing |
| 142 | +----------------- |
| 143 | + |
| 144 | +Finding length of string |
| 145 | +~~~~~~~~~~~~~~~~~~~~~~~~ |
| 146 | + |
| 147 | +In SPSS: |
| 148 | + |
| 149 | +.. code-block:: text |
| 150 | +
|
| 151 | + COMPUTE length = LENGTH(time). |
| 152 | + EXECUTE. |
| 153 | +
|
| 154 | +.. include:: includes/length.rst |
| 155 | + |
| 156 | + |
| 157 | +Changing case |
| 158 | +~~~~~~~~~~~~~ |
| 159 | + |
| 160 | +In SPSS: |
| 161 | + |
| 162 | +.. code-block:: text |
| 163 | +
|
| 164 | + COMPUTE upper = UPCASE(time). |
| 165 | + COMPUTE lower = LOWER(time). |
| 166 | + EXECUTE. |
| 167 | +
|
| 168 | +.. include:: includes/case.rst |
| 169 | + |
| 170 | + |
| 171 | +Merging |
| 172 | +------- |
| 173 | + |
| 174 | +In SPSS, merging data files is done through Data > Merge Files. |
| 175 | + |
| 176 | +.. include:: includes/merge_setup.rst |
| 177 | +.. include:: includes/merge.rst |
| 178 | + |
| 179 | + |
| 180 | +GroupBy operations |
| 181 | +------------------ |
| 182 | + |
| 183 | +Split-file processing |
| 184 | +~~~~~~~~~~~~~~~~~~~~~ |
| 185 | + |
| 186 | +In SPSS, split-file analysis is done through Data > Split File: |
| 187 | + |
| 188 | +.. code-block:: text |
| 189 | +
|
| 190 | + SORT CASES BY sex. |
| 191 | + SPLIT FILE BY sex. |
| 192 | + DESCRIPTIVES VARIABLES=total_bill tip |
| 193 | + /STATISTICS=MEAN STDDEV MIN MAX. |
| 194 | +
|
| 195 | +The pandas equivalent would be: |
| 196 | + |
| 197 | +.. code-block:: python |
| 198 | +
|
| 199 | + tips.groupby("sex")[["total_bill", "tip"]].agg(["mean", "std", "min", "max"]) |
| 200 | +
|
| 201 | +
|
| 202 | +Missing data |
| 203 | +------------ |
| 204 | + |
| 205 | +SPSS uses the period (``.``) for numeric missing values and blank spaces for string missing values. |
| 206 | +pandas uses ``NaN`` (Not a Number) for numeric missing values and ``None`` or ``NaN`` for string |
| 207 | +missing values. |
| 208 | + |
| 209 | +.. include:: includes/missing.rst |
| 210 | + |
| 211 | + |
| 212 | +Other considerations |
| 213 | +-------------------- |
| 214 | + |
| 215 | +Output management |
| 216 | +----------------- |
| 217 | + |
| 218 | +While pandas does not have a direct equivalent to SPSS's Output Management System (OMS), you can |
| 219 | +capture and export results in various ways: |
| 220 | + |
| 221 | +.. code-block:: python |
| 222 | +
|
| 223 | + # Save summary statistics to CSV |
| 224 | + tips.groupby('sex')[['total_bill', 'tip']].mean().to_csv('summary.csv') |
| 225 | +
|
| 226 | + # Save multiple results to Excel sheets |
| 227 | + with pd.ExcelWriter('results.xlsx') as writer: |
| 228 | + tips.describe().to_excel(writer, sheet_name='Descriptives') |
| 229 | + tips.groupby('sex').mean().to_excel(writer, sheet_name='Means by Gender') |
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