NAG C Library Function Document

nag_tabulate_margin (g11bcc) computes a marginal table from a table computed by nag_tabulate_stats (g11bac) or nag_tabulate_percentile (g11bbc) using a selected statistic.

2

Specification

#include <nag.h>

#include <nagg11.h>

void	nag_tabulate_margin (Nag_TableStats stat, const double table[], Integer ncells, Integer ndim, const Integer idim[], const Integer isdim[], double sub_table[], Integer maxst, Integer mcells, Integer mdim, Integer mlevel[], double comm_ar[], NagError *fail)

3

Description

For a dataset containing classification variables (known as factors) the functions nag_tabulate_stats (g11bac) and nag_tabulate_percentile (g11bbc) compute a table using selected statistics, for example the mean or the median. The table is indexed by the levels of the selected factors, for example if there were three factors A, B and C with

3

2

and

4

levels respectively and the mean was to be tabulated the resulting table would be

3 \times 2 \times 4

with each cell being the mean of all observations with the appropriate combination of levels of the three factors. In further analysis the table of means averaged over C for A and B may be required; this can be computed from the full table by taking the mean over the third dimension of the table, C.

In general, given a table computed by nag_tabulate_stats (g11bac) or nag_tabulate_percentile (g11bbc), nag_tabulate_margin (g11bcc) computes a sub-table defined by a subset of the factors used to define the table such that each cell of the sub-table is the selected statistic computed over the remaining factors. The statistics that can be used are the total, the mean, the median, the variance, the smallest and the largest value.

4

References

John J A and Quenouille M H (1977) Experiments: Design and Analysis Griffin

Kendall M G and Stuart A (1969) The Advanced Theory of Statistics (Volume 1) (3rd Edition) Griffin

West D H D (1979) Updating mean and variance estimates: An improved method Comm. ACM 22 532–555

5

Arguments

1: $stat$ – Nag_TableStatsInput

On entry: indicates which statistic is to be used to compute the marginal table.

$stat = Nag_TableStatsNObs$: The total.
$stat = Nag_TableStatsAv$: The average or mean.
$stat = Nag_TableStatsMedian$: The median.
$stat = Nag_TableStatsVar$: The variance.
$stat = Nag_TableStatsLarge$: The largest value.
$stat = Nag_TableStatsSmall$: The smallest value.

Constraint:

stat = Nag_TableStatsNObs

Nag_TableStatsAv

Nag_TableStatsMedian

Nag_TableStatsVar

Nag_TableStatsLarge

Nag_TableStatsSmall

2: $table [ncells]$ – const doubleInput

On entry: the table as computed by nag_tabulate_stats (g11bac) or nag_tabulate_percentile (g11bbc).

3: $ncells$ – IntegerInput

On entry: the number of cells in table as returned by nag_tabulate_stats (g11bac) or nag_tabulate_percentile (g11bbc).

4: $ndim$ – IntegerInput

On entry: the number of dimensions for table as returned by nag_tabulate_stats (g11bac) or nag_tabulate_percentile (g11bbc).

Constraint:

ndim \geq 2

5: $idim [ndim]$ – const IntegerInput

On entry: the number of levels for each dimension of table as returned by nag_tabulate_stats (g11bac) or nag_tabulate_percentile (g11bbc).

Constraint:

idim [i] \geq 2

, for

i = 0, 1, \dots, ndim - 1

6: $isdim [ndim]$ – const IntegerInput

On entry: indicates which dimensions of table are to be included in the sub-table. If

isdim [i - 1] > 0

the dimension or factor indicated by

idim [i - 1]

is to be included in the sub-table, otherwise it is excluded.

7: $sub_table [maxst]$ – doubleOutput

On exit: the first mcells elements contain the sub-table computed using the statistic indicated by stat. The table is stored in a similar way to table with the mcells cells stored so that for any two dimensions the index relating to the dimension given later in idim changes faster. For further details see Section 9.

8: $maxst$ – IntegerInput

On entry: the maximum size of sub-table to be computed.

Constraint:

maxst \geq

the product of the levels of the dimensions of table included in the sub-table, sub_table.

9: $mcells$ – Integer *Output

On exit: the number of cells in the sub-table in sub_table.

10: $mdim$ – Integer *Output

On exit: the number of dimensions to the sub-table in sub_table.

11: $mlevel [ndim]$ – IntegerOutput

On exit: the first mdim elements contain the number of levels for the dimensions of the sub-table in sub_table. The remaining elements are not referenced.

12: $comm_ar [\dim]$ – doubleOutput

Note: the dimension, dim, of the array comm_ar must be at least

$maxst$ when $stat = Nag_TableStatsVar$ ;
$1$ otherwise.

On exit: if

stat = Nag_TableStatsVar

comm_ar contains the sub-table of means corresponding to the sub-table of variances in sub_table. Otherwise comm_ar is not referenced.

13: $fail$ – NagError *Input/Output

The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

6

Error Indicators and Warnings

NE_ALLOC_FAIL: Dynamic memory allocation failed.
See Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.
NE_BAD_PARAM: On entry, argument $〈value〉$ had an illegal value.
NE_INT: On entry, $i = 〈value〉$ and $idim [i - 1] = 〈value〉$ .
Constraint: $idim \geq 2$ .

On entry, $ndim = 〈value〉$ .
Constraint: $ndim \geq 2$ .
NE_INT_2: On entry, $maxst = 〈value〉$ and minimum value for $maxst = 〈value〉$ .
Constraint: $maxst \geq product$ of the levels of the dimensions of the table included in the sub-table, sub_table.

On entry, ncells is incompatible with idim.
NE_INT_ARRAY_ELEM_CONS: On entry, all elements of $isdim > 0$ .

On entry, no elements of $isdim > 0$ .
NE_INTERNAL_ERROR: An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
See Section 2.7.6 in How to Use the NAG Library and its Documentation for further information.
NE_NO_LICENCE: Your licence key may have expired or may not have been installed correctly.
See Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.

7

Accuracy

Only applicable when

stat = Nag_TableStatsVar

. In this case a one pass algorithm is used as describe in West (1979).

8

Parallelism and Performance

nag_tabulate_margin (g11bcc) is threaded by NAG for parallel execution in multithreaded implementations of the NAG Library.

Please consult the x06 Chapter Introduction for information on how to control and interrogate the OpenMP environment used within this function. Please also consult the Users' Note for your implementation for any additional implementation-specific information.

9

Further Comments

The sub-tables created by nag_tabulate_margin (g11bcc) and stored in sub_table and, depending on stat, also in comm_ar are stored in the following way. Let there be

m

dimensions defining the table with dimension

k

having

l_{k}

levels, then the cell defined by the levels

i_{1}, i_{2}, \dots, i_{m}

of the factors is stored in

s

th cell given by

s = 1 + \sum_{k = 1}^{m} [(i_{k} - 1) c_{k}],

where

c_{j} = \prod_{k = j + 1}^{m} l_{k} for ​ j = 1, 2, \dots, n - 1 and c_{m} = 1 .

10

Example

The data, given by John and Quenouille (1977), is for

3

blocks of a

3 \times 6

factorial experiment. The data can be considered as a

3 \times 6 \times 3

table (i.e., blocks

\times

treatment with

6

levels

\times

treatment with

3

levels). This table is input and the

6 \times 3

table of treatment means for over blocks is computed and printed.

NAG C Library Function Document

nag_tabulate_margin (g11bcc)

▸▿ Contents

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

6 Error Indicators and Warnings

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results

1

Purpose

2

Specification

3

Description

4

References

5

Arguments

6

Error Indicators and Warnings

7

Accuracy

8

Parallelism and Performance

9

Further Comments

10

Example

10.1

Program Text

10.2

Program Data

10.3

Program Results