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IDL REFERENCE MANUAL
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IDL REFERENCE MANUAL
The Interactive Data-analysis Language
Reference Manual
BY Ronald M. Kaplan, B. A. Sheil AND Eliot R. Smith
DECEMBER 1978
SSL-1978-4
XEROX
PALO ALTO RESEARCH CENTER
3333 Coyote Hill Road / Palo Alto / California 94304
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ABSTRACT
This document describes a computer system for the analysis of data from experiments and observational studies of the type carried out by social scientists. Initially developed at Harvard University, the version described here is an Interlisp implementation carried out at the Palo Alto Research Center of the Xerox Corporation.
Unlike most data analysis systems, IDL is constructed around a set of "basis operators" for data analysis, and emphasizes their combination to mould operators to match the user’s tasks, rather than the provision of pre-programmed ones. This implementation is a test bed both for this philosophy of application programming and also for the specific decomposition of linear statistics which it contains. Comments and interested users are most welcome.
KEY WORDS AND PHRASES
Data analysis, linear statistics, Interlisp, interactive systems, application programming.
CAVEAT
Both this manual and the system which it describes are, and will remain for the indefinite future, in a state of development. Although we both solicit and welcome users and will support them with consultation, bug fixes, and new features to the extent permitted by our other activities, we can guarantee neither the performance of the system, the validity of its results, nor the accuracy of its documentation.
BECOMING A USER
Anyone wishing to become a user of IDL is advised to contact one of the authors, so that their name can be added to the distribution list for announcements of new releases, facilities, and documentation. Specific instructions for accessing IDL on the Maxc2 time-sharing system can be found in Appendix A.
CONTENTS
0. Introduction
1. The philosophy of IDL1
2. The relation between IDL and Interlisp2
3. The rest of this manual4
1. Data representation
1. Array structure5
2. Terminology6
3. Labels6
4. Missing data7
5. Large arrays7
6. Function extension7
7. Conversion from other representations8
2. System facilities
1. Selection11
1. Elements11
2. Other array properties14
2. Assignment15
3. Function extension16
1. Single argument functions17
2. Multiple argument functions18
3. Affecting the decomposition (KEEP and LEAVE)20
4. User-written functions22
4. Printing23
3. Arithmetic and mathematical functions
1. Arithmetic operators25
2. Constants25
3. Mathematical and trigonometric functions25
4. Distribution functions26
5. RAND and RANDN26
6. ROUND26
7. SAME26
8. TRANSLATE27
4. Array functions
1. ADJOIN29
2. DEAL29
3. FORMAT and ELEMENTTYPE29
4. GENVEC30
5. IDLARRAYP30
6. INVERT30
7. MPROD30
8. ORDER31
9. RANK31
10. REDUCE, RPLUS, RTIMES31
11. RESHAPE32
12. SEEK32
13. SHAPE32
14. SHIFT32
15. TRANSPOSE33
5. Compression functions
1. COUNTS35
2. COVAR35
3. GROUP36
4. MOMENTS37
5. PAIRN37
6. POOL37
6. Analysis functions
1. ANOVA39
2. EMS40
3. HIST40
4. PLOT41
5. NORM41
6. SWEEP41
7. Data input and output
1. To and from list structure43
2. To and from files45
8. Data analysis with IDL
1. Ante data47
1. Experimental design47
2. Artificial data generation48
2. Data49
1. Data entry49
2. Recoding49
3. Weighting50
4. Subsetting50
3. Correlational statistics52
1. Covariance and correlation52
2. Regression53
1. Unstandardized regression53
2. Standardized regression55
3. Regression residuals55
4. Partial correlation55
4. Classification based statistics56
1. Frequency statistics56
2. Measure statistics58
1. Non-parametric methods58
2. Parametric methods (ANOVA)60
APPENDICES
A. The IDL environment[Not included]
B. The IDL library65
C. List of global variables and their initial values67
D. Summary list of IDL functions69
E. Technical considerations75
F. A sample protocol77
Glossary95
References99
ACKNOWLEDGEMENTS
IDL was initially designed by Beau Sheil and Eliot Smith under the auspices of the Computation Facility of the Center for Behavioral Sciences at Harvard University during 1974. That development was largely supported by a grant to the Center from the Harvard University Faculty of Arts and Sciences, and by computing resources made available by the Harvard University Center for Research in Computing Technology. The work profited greatly from the enthusiastic support and technical guidance of Dr. Klaus Allerbeck, at that time Director of the Computation Facility, and many others who provided advice and encouragement, including Karen Lease, Thomas Cheatham, Ronald Kaplan, David Kenny, and Joanne Martin.
The design was revised and extended by Ron Kaplan and Beau Sheil at Xerox Palo Alto Research Center, where the Interlisp implementation was carried out. Our thanks to Jan Derksen, Warren Teitelman, and Larry Masinter for all their help and assistance, and to our respective Laboratories for supporting this effort.