Add C example for indexing

.gitignore

@@ -211,6 +211,7 @@ include
 
 #from make
 examples/C/check_gaussian_grid
+examples/C/ensemble_index
 examples/C/clone
 examples/C/iterator_bitmap
 examples/C/new_sample

examples/C/CMakeLists.txt

@@ -31,6 +31,7 @@ list( APPEND test_bins
       large_grib1
       clone
       check_gaussian_grid
+      ensemble_index
 )
 foreach( tool ${test_bins} )
     ecbuild_add_executable( TARGET    ${tool}

examples/C/Makefile.am

@@ -7,7 +7,7 @@ TESTS = iterator.sh get.sh print_data.sh set.sh keys_iterator.sh multi.sh multi_
 noinst_PROGRAMS  = nearest set_bitmap iterator get print_data set set_missing keys_iterator \
                    set_data mars_param values_check box multi multi2 multi_write precision \
                    set_pv list sections_copy large_grib1 get_data iterator_bitmap clone new_sample \
-                   check_gaussian_grid
+                   check_gaussian_grid ensemble_index
 bin_PROGRAMS            = points
 
 box_SOURCES             = box.c
@@ -35,6 +35,7 @@ get_data_SOURCES        = get_data.c
 clone_SOURCES           = clone.c
 new_sample_SOURCES      = new_sample.c
 check_gaussian_grid_SOURCES = check_gaussian_grid.c
+ensemble_index_SOURCES = ensemble_index.c
 
 INCLUDES =  -I$(top_builddir)/src
 

examples/C/ensemble_index.c

@@ -0,0 +1,121 @@
+/*
+ * Copyright 2005-2014 ECMWF.
+ *
+ * This software is licensed under the terms of the Apache Licence Version 2.0
+ * which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * In applying this licence, ECMWF does not waive the privileges and immunities granted to it by
+ * virtue of its status as an intergovernmental organisation nor does it submit to any jurisdiction.
+ */
+
+/*
+ * Description: index a GRIB file, select 2t and compute ensemble mean.
+ *
+ */
+
+#include "grib_api.h"
+
+int main(int argc, char * argv[])
+{
+    int ret;
+    int i, j;
+    int count=0;
+    size_t paramIdSize, numberSize, values_len;
+    char** paramId;
+    long* number;
+    double* values;
+    double* result=NULL;
+    double min=1000,max=0,avg=0;
+    grib_index* index;
+    grib_handle* h=NULL;
+
+    /* create index of file contents for paramId and number */
+    index = grib_index_new_from_file(0, "eps", "paramId,number",&ret);
+    GRIB_CHECK(ret,0);
+
+    /* get size of "paramId" list */
+    GRIB_CHECK(grib_index_get_size(index, "paramId", &paramIdSize),0);
+    printf("grib contains %ld different parameters\n",paramIdSize);
+    /* allocate memory for "paramId" list */
+    paramId = (char**) malloc(paramIdSize * sizeof(char*));
+    /* get list of "paramId" */
+    GRIB_CHECK(grib_index_get_string(index, "paramId", paramId, &paramIdSize),0);
+
+    /* get size of ensemble number list */
+    GRIB_CHECK(grib_index_get_size(index, "number", &numberSize),0);
+    printf("grib contains %ld different ensemble members\n",numberSize);
+    /* allocate memory for ensemble number list */
+    number = (long*) malloc(numberSize * sizeof(long));
+    /* get list of ensemble numbers */
+    GRIB_CHECK(grib_index_get_long(index, "number", number, &numberSize),0);
+
+    /* select T850 with paramId 130 */
+    GRIB_CHECK(grib_index_select_string(index, "paramId", "130"), 0);
+
+    /* loop over all members */
+    for (i = 0; i < numberSize; i++) {
+        count++;
+        /* select an individual ensemble number */
+        GRIB_CHECK(grib_index_select_long(index, "number", number[i]), 0);
+
+        /* create handle for next grib message */
+        h=grib_handle_new_from_index(index, &ret);
+        if (ret) {
+            printf("error: %d\n", ret);
+            exit(ret);
+        }
+
+        /* get the size of the values array */
+        GRIB_CHECK(grib_get_size(h, "values", &values_len), 0);
+
+        /* allocate memory for the grib message */
+        values = malloc(values_len * sizeof(double));
+
+        /* allocate memory for result */
+        if ( i == 0 ) {
+            result = (double *)calloc(values_len, sizeof(double));
+        }
+
+        /* get data values */
+        GRIB_CHECK(grib_get_double_array(h, "values", values, &values_len), 0);
+
+        /* add up values */
+        for (j = 0; j < values_len; j++)
+            result[j] = result[j] + values[j];
+
+        /* free memory and grib message handle */
+        free(values);
+        GRIB_CHECK(grib_handle_delete(h), 0);
+    }
+
+    printf("We considered %d ensemble members\n", count);
+
+    for (j = 0; j < values_len; j++)
+        result[j] = result[j] / count;
+
+    for (j = 0; j < values_len; j++) {
+        if (min > result[j]) {
+            min = result[j];
+        }
+        if (max < result[j]) {
+            max = result[j];
+        }
+        avg += result[j];
+    }
+    avg = avg/values_len;
+
+    printf("==============================================================================\n");
+    printf("Stats for ensemble mean of T850\n");
+    printf("Min: %f Max: %f Avg: %f\n",min,max,avg);
+    printf("==============================================================================\n");
+
+    /* finally free all other memory */
+    for (i=0;i<paramIdSize;i++)
+        free(paramId[i]);
+    free(paramId);
+    free(number);
+    free(result);
+    grib_index_delete(index);
+
+    return 0;
+}