## #474 closed defect (fixed)

# r.quantile: segfaults with percentile=100

Reported by: | hamish | Owned by: | |
---|---|---|---|

Priority: | major | Milestone: | 6.4.0 |

Component: | Raster | Version: | svn-develbranch6 |

Keywords: | r.quantile | Cc: | |

CPU: | x86-32 | Platform: | Linux |

### Description

spearfish:

g.region rast=elevation.10m r.quantile elevation.10m percentile=0,10,20,30,40,50,60,70,80,90,100 Computing histogram 100% Computing bins Binning data 100% Sorting bins 100% Computing quantiles 0:0.000000:1061.064087 1:10.000000:1159.293774 2:20.000000:1184.320190 3:30.000000:1210.821362 4:40.000000:1251.937646 5:50.000000:1309.368164 6:60.000000:1378.708764 7:70.000000:1440.232398 8:80.000000:1525.849707 9:90.000000:1613.602832 Segmentation fault

gdb:

Program received signal SIGSEGV, Segmentation fault. 0x08049205 in compute_quantiles (recode=0) at main.c:209 209 v = (i0 == i1) (gdb) bt #0 0x08049205 in compute_quantiles (recode=0) at main.c:209 #1 0x0804975c in main (argc=0, argv=0x3ff00000) at main.c:326 (gdb) list 204 205 k = next - b->origin; 206 i0 = (int)floor(k); 207 i1 = (int)ceil(k); 208 209 v = (i0 == i1) 210 ? values[b->base + i0] 211 : values[b->base + i0] * (i1 - k) + values[b->base + i1] * (k - 212 i0); 213 (gdb) bt full #0 0x08049205 in compute_quantiles (recode=0) at main.c:209 k = 2654489 i1 = 2654489 next = 2654802 v = 1613.6028318000001 i0 = 2654489 b = (struct bin *) 0x805e9e4 prev_v = 1613.6028318000001 quant = 10 #1 0x0804975c in main (argc=0, argv=0x3ff00000) at main.c:326 module = (struct GModule *) 0xb7f3f170 opt = {input = 0xb7f3f120, quant = 0x804b028, perc = 0x804b088, slots = 0x804b0e8} flag = {r = 0xb7f3f0fc} recode = 0 infile = 6 range = {min = 1061.064087, max = 1846.743408, first_time = 0}

presumably values[b->base + i0] is just outside the array.

Hamish

### Change History (5)

### comment:1 follow-up: 4 Changed 13 years ago by

### comment:3 Changed 13 years ago by

Resolution: | → fixed |
---|---|

Status: | new → closed |

thanks, works.

I notice it does not exactly match r.univar,

G65> r.quantile in=elevation.10m percentile=`seq -s, 0 10 100` 0:0.000000:1061.064087 1:10.000000:1153.037231 2:20.000000:1184.320190 3:30.000000:1210.821362 4:40.000000:1251.937646 5:50.000000:1309.368164 6:60.000000:1378.708764 7:70.000000:1440.232398 8:80.000000:1525.849707 9:90.000000:1613.602832 10:100.000000:1846.743408

G65> r.univar -ge elevation.10m percentile=`seq -s, 0 10 100` percentile_0=1061.06 percentile_10=1153.04 percentile_20=1184.32 percentile_30=1210.82 percentile_40=1251.94 percentile_50=1309.37 percentile_60=1378.71 percentile_70=1440.23 percentile_80=1525.85 percentile_90=1613.6 percentile_100=1846.74

because r.univar's output has been rounded by %g at very few digits.. (see trac #335). otherwise it matches fine.

closing bug.

Hamish

### comment:4 follow-up: 5 Changed 13 years ago by

Replying to glynn:

This also fixes a bug where the quantile corresponds to the last value in the bin (e.g. if there is only one value in the bin). The interpolation will use the first value from the bin for the next quantile, which could be way off.

I notice that if you do 'quant=3' you only get 2 results, and 'quant=1' gives no output. (all others do the same, report n-1)

Is this intended because 3 bins will have two separators (at 33% and 66%), or is it a bug?

Hamish

### comment:5 Changed 13 years ago by

Replying to hamish:

I notice that if you do 'quant=3' you only get 2 results, and 'quant=1' gives no output. (all others do the same, report n-1)

Is this intended because 3 bins will have two separators (at 33% and 66%), or is it a bug?

It's intended so that quant=N gives "N-tiles", e.g. quant=4 gives quartiles, quant=10 gives deciles, etc. AIUI, the convention is not to include the endpoints, e.g. "quartiles" are given as 25%, 50%, and 75%.

**Note:**See TracTickets for help on using tickets.

Replying to hamish:

Actually, it's way outside the array, as the last bin never gets initialised.

Hopefully fixed in r35846.

This also fixes a bug where the quantile corresponds to the last value in the bin (e.g. if there is only one value in the bin). The interpolation will use the first value from the bin for the next quantile, which could be way off.

Ideally, it should retain the values from the following bin in case one is needed for interpolation. In practice, this won't make much difference.