diff options
| author | Luca Deri <deri@ntop.org> | 2022-04-04 10:02:45 +0200 |
|---|---|---|
| committer | Luca Deri <deri@ntop.org> | 2022-04-04 10:02:45 +0200 |
| commit | a6e2f4a15a52087ff3f2fa16bb990c998c5215a6 (patch) | |
| tree | f8b5470e3cd1f620b5861455285fae5d2a1c4dfe /src/lib | |
| parent | 19019383f0ca4262c43af30b8de9a96413f9534e (diff) | |
Added ndpi_find_outliers() API call using Z-Score
Diffstat (limited to 'src/lib')
| -rw-r--r-- | src/lib/ndpi_analyze.c | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/src/lib/ndpi_analyze.c b/src/lib/ndpi_analyze.c index beb6ca750..ebb5617ef 100644 --- a/src/lib/ndpi_analyze.c +++ b/src/lib/ndpi_analyze.c @@ -161,6 +161,16 @@ float ndpi_data_stddev(struct ndpi_analyze_struct *s) { /* ********************************************************************************* */ +/* + Compute the mean on all values + NOTE: In statistics, there is no difference between the mean and average +*/ +float ndpi_data_mean(struct ndpi_analyze_struct *s) { + return(ndpi_data_average(s)); +} + +/* ********************************************************************************* */ + /* Compute the average only on the sliding window */ float ndpi_data_window_average(struct ndpi_analyze_struct *s) { if(s->num_values_array_len) { @@ -1425,3 +1435,35 @@ void ndpi_des_fitting(double *values, u_int32_t num_values, float *ret_alpha, fl *ret_alpha = best_alpha, *ret_beta = best_beta; } + +/* *********************************************************** */ + +/* Z-Score = (Value - Mean) / StdDev */ +u_int ndpi_find_outliers(u_int32_t *values, bool *outliers, u_int32_t num_values) { + u_int i, ret = 0; + float mean, stddev, low_threshold = -2.5, high_threshold = 2.5; + struct ndpi_analyze_struct a; + + ndpi_init_data_analysis(&a, 3 /* this is the window so we do not need to store values and 3 is enough */); + + /* Add values */ + for(i=0; i<num_values; i++) + ndpi_data_add_value(&a, values[i]); + + mean = ndpi_data_mean(&a); + stddev = ndpi_data_stddev(&a); + + /* Process values */ + for(i=0; i<num_values; i++) { + float z_score = (((float)values[i]) - mean) / stddev; + bool is_outlier = ((z_score < low_threshold) || (z_score > high_threshold)) ? true : false; + + if(is_outlier) ret++; + outliers[i] = is_outlier; + } + + ndpi_free_data_analysis(&a, 0); + + return(ret); +} + |