g11bac (tabulate_stat) : NAG Library CL Interface, Mark 27

2 Specification

#include <nag.h>

void

g11bac (Nag_TableStats stat, Nag_TableUpdate update, Nag_Weightstype weight, Integer n, Integer nfac, const Integer sf[], const Integer lfac[], const Integer factor[], Integer tdf, const double y[], const double wt[], double table[], Integer maxt, Integer *ncells, Integer *ndim, Integer idim[], Integer count[], double comm_ar[], NagError *fail)

The function may be called by the names: g11bac, nag_contab_tabulate_stat or nag_tabulate_stats.

3 Description

A dataset may include both classification variables and general variables. The classification variables, known as factors, take a small number of values known as levels. For example, the factor sex would have the levels male and female. These can be coded as 1 and 2 respectively. Given several factors, a multi-way table can be constructed such that each cell of the table represents one level from each factor. For example, the two factors sex and habitat, habitat having three levels: inner-city, suburban and rural, define the 2 by 3 contingency table:

Sex	Habitat
	Inner-city	Suburban	Rural
Male
Female

For each cell statistics can be computed. If a third variable in the dataset was age, then for each cell the average age could be computed:

Sex	Habitat
	Inner-city	Suburban	Rural
Male	25.5	30.3	35.6
Female	23.2	29.1	30.4

That is the average age for all observations for males living in rural areas is

35.6

. Other statistics can also be computed: the number of observations, the total, the variance, the largest value and the smallest value.

g11bac computes a table for one of the selected statistics. The factors have to be coded with levels

1, 2, \dots

. Weights can be used to eliminate values from the calculations, e.g., if they represent ‘missing values’. There is also the facility to update an existing table with the addition of new observations.

5 Arguments

stat

– Nag_TableStats Input

On entry: indicates which statistic is to be computed for the table cells.

$stat = Nag_TableStatsNObs$: The number of observations for each cell.
$stat = Nag_TableStatsTotal$: The total for the variable in y for each cell.
$stat = Nag_TableStatsAv$: The average (mean) for the variable in y for each cell.
$stat = Nag_TableStatsVar$: The variance for the variable in y for each cell.
$stat = Nag_TableStatsLarge$: The largest value for the variable in y for each cell.
$stat = Nag_TableStatsSmall$: The smallest value for the variable in y for each cell.

Constraint:

stat = Nag_TableStatsNObs

Nag_TableStatsTotal

Nag_TableStatsAv

Nag_TableStatsVar

Nag_TableStatsLarge

Nag_TableStatsSmall

update

– Nag_TableUpdate Input

On entry: indicates if an existing table is to be updated by further observation.

$update = Nag_TableUpdateI$: The table cells will be initialized to zero before tabulations take place.
$update = Nag_TableUpdateU$: The table input in table will be updated. The arguments ncells, table, count and comm_ar must remain unchanged from the previous call to g11bac.

Constraint:

update = Nag_TableUpdateI

Nag_TableUpdateU

weight

– Nag_Weightstype Input

On entry: indicates if weights are to be used.

$weight = Nag_NoWeights$: Weights are not used and unit weights are assumed.
$weight = Nag_Weights$ or $Nag_Weightsvar$: Weights are used and must be supplied in wt. The only difference between $weight = Nag_Weights$ and $weight = Nag_Weightsvar$ is if the variance is computed.
$weight = Nag_Weights$: The divisor for the variance is the sum of the weights minus one and if $weight = Nag_Weightsvar$ , the divisor is the number of observations with nonzero weights minus one. The former is useful if the weights represent the frequency of the observed values.

stat = Nag_TableStatsTotal

Nag_TableStatsAv

, the weighted total or mean is computed respectively.

stat = Nag_TableStatsNObs

Nag_TableStatsLarge

Nag_TableStatsSmall

the only effect of weights is to eliminate values with zero weights from the computations.

Constraint:

weight = Nag_NoWeights

Nag_Weightsvar

Nag_Weights

n

– Integer Input

On entry: the number of observations.

Constraint:

n \geq 2

nfac

– Integer Input

On entry: the number of classifying factors in factor.

Constraint:

nfac \geq 1

sf [nfac]

– const Integer Input

On entry: indicates which factors in factor are to be used in the tabulation.

sf [i - 1] > 0

the

i

th factor in factor is included in the tabulation.

Note that if

sf [i - 1] \leq 0

for

i = 1, 2, \dots, nfac

then the statistic for the whole sample is calculated and returned in a 1 by 1 table.

lfac [nfac]

– const Integer Input

On entry: the number of levels of the classifying factors in factor.

Constraint: if

sf [i - 1] > 0

lfac [i - 1] \geq 2

, for

i = 1, 2, \dots, nfac

factor [n \times tdf]

– const Integer Input

On entry: the nfac coded classification factors for the n observations.

Constraint:

1 \leq factor [(i - 1) \times tdf + j - 1] \leq lfac [j - 1]

, for

i = 1, 2, \dots, n

and

j = 1, 2, \dots, nfac

tdf

– Integer Input

On entry: the stride separating matrix column elements in the array factor.

Constraint:

tdf \geq nfac

10:

y [n]

– const double Input

On entry: the variable to be tabulated.

stat = Nag_TableStatsNObs

, y is not referenced.

11:

wt [n]

– const double Input

On entry: if

weight = Nag_Weights

Nag_Weightsvar

, wt must contain the n weights. Otherwise wt is not referenced and can be set to null, (double *)0.

Constraint: if

weight = Nag_Weights

Nag_Weightsvar

wt [i - 1] \geq 0.0

, for

i = 1, 2, \dots, n

12:

table [maxt]

– double Input/Output

On entry: if

update = Nag_TableUpdateU

, table must be unchanged from the previous call to g11bac, otherwise table need not be set.

On exit: the computed table. The ncells cells of the table are stored so that for any two factors the index relating to the factor referred to later in lfac and factor changes faster. For further details see Section 9.

13:

maxt

– Integer Input

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

Constraint:

maxt \geq

product of the levels of the factors included in the tabulation.

14:

ncells

– Integer * Input/Output

On entry: if

update = Nag_TableUpdateU

, ncells must be unchanged from the previous call to g11bac, otherwise ncells need not be set.

On exit: the number of cells in the table.

15:

ndim

– Integer * Output

On exit: the number of factors defining the table.

16:

idim [nfac]

– Integer Output

On exit: the first ndim elements contain the number of levels for the factors defining the table.

17:

count [maxt]

– Integer Input/Output

On entry: if

update = Nag_TableUpdateU

, count must be unchanged from the previous call to g11bac, otherwise count need not be set.

On exit: a table containing the number of observations contributing to each cell of the table, stored identically to table. Note if

stat = Nag_TableStatsNObs

this is the same as is returned in table.

18:

comm_ar [*]

– double Input/Output

On entry: if

update = Nag_TableUpdateU

, comm_ar must be unchanged from the previous call to g11bac, otherwise comm_ar need not be set.

On exit: if

stat = Nag_TableStatsAv

Nag_TableStatsVar

, the first ncells values hold the table containing the sum of the weights for the observations contributing to each cell, stored identically to table. If

stat = Nag_TableStatsVar

, then the second set of ncells values hold the table of cell means. Otherwise comm_ar is not referenced.

19:

fail

– NagError * Input/Output

The NAG error argument (see Section 7 in the Introduction to the NAG Library CL Interface).

6 Error Indicators and Warnings

NE_2_INT_ARG_LT

On entry,

tdf = 〈value〉

while

nfac = 〈value〉

. These arguments must satisfy

tdf \geq nfac

NE_2_INT_ARRAY_CONS

On entry,

sf [〈value〉] = 〈value〉

while

lfac [0] = 〈value〉

.
Constraint: if

sf [i] > 0

lfac [i] \geq 2

for

i = 0, 1, \dots, nfac

NE_2D_1D_INT_ARRAYS_CONS

On entry,

factor [(〈value〉) \times tdf + 〈value〉] = 〈value〉

while

lfac [0] = 〈value〉

.
Constraint:

factor [(i) \times tdf + j] \leq lfac [j]

, for

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

and

j = 0, 1, \dots, nfac - 1

NE_2D_INT_ARRAY_CONS

On entry,

factor [(〈value〉) \times tdf + 〈value〉] = 〈value〉

.
Constraint:

factor [(i) \times tdf + j] \geq 1

, for

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

and

j = 0, 1, \dots, nfac - 1

NE_ALLOC_FAIL

Dynamic memory allocation failed.

NE_BAD_PARAM

On entry, argument stat had an illegal value.

On entry, argument update had an illegal value.

On entry, argument weight had an illegal value.

NE_G11BA_CHANGED

update = Nag_TableUpdateU

and at least one of ncells, table, comm_ar or count have been changed since previous call to g11bac.

NE_INT_ARG_LT

On entry,

n = 〈value〉

.
Constraint:

n \geq 2

On entry,

nfac = 〈value〉

.
Constraint:

nfac \geq 1

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.

NE_MAXT

The maximum size of the table to be computed, maxt is too small.

NE_REAL_ARRAY_CONS

On entry,

wt [〈value〉] = 〈value〉

.
Constraint: if

weight = Nag_Weights

Nag_Weightsvar

wt [i] \geq 0.0

NE_VAR_DIV

stat = Nag_TableStatsVar

and the divisor for the variance

\leq 0.0

NE_WT_ARGS

The wt array argument must not be NULL when the weight argument indicates weights.

9 Further Comments

The tables created by g11bac and stored in table, count and, depending on stat, also in comm_ar are stored in the following way. Let there be

n

factors defining the table with factor

k

having

l_{k}

levels, then the cell defined by the levels

i_{1}

i_{2}, \dots, i_{n}

of the factors is stored in

m

th cell given by:

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

where

c_{j} = \prod_{k = j + 1}^{n} l_{k}

, for

j = 1, 2, \dots, n - 1

and

c_{n} = 1

NAG CL Interface
g11bac (tabulate_stat)

▸▿ 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

NAG CL Interfaceg11bac (tabulate_​stat)

▸▿ 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

NAG CL Interface
g11bac (tabulate_stat)