cl-data-frame pretty printed column summaries

I have been refining printed summaries of data frames for my Common Lisp library cl-data-frame. I found that the following approach works best for me for quick eyeballing of data before any processing or analysis:

1. Real numbers should be summarized by their range and the three quartiles (25%, 50%, 75%). This provides enough information to assess the variation and the "typical" values of the data.
2. All other values should be summarized by their count and frequency. This is ideal for categorical data (called "factor" in R), and also for various encodings of missing data.
3. When the column has both numbers and non-numbers, print both of the above. However, when it has very few distinct numbers, don't use quartiles for numbers, just print the frequencies.

For example,

(dframe:df :a #(nil nil nil 1 1 2 3 "missing" "missing"))

prints as

#<CL-DATA-FRAME:DATA-FRAME (1 x 7)
  :A 3 (43%) x NIL, 2 (29%) x 1, 1 (14%) x 2, 1 (14%) x 3>

while

(dframe:df :a (concatenate 'vector
                           #(nil nil nil "missing" "missing")
                           (clnu:numseq 0 100 :by 1/100)))

prints as

#<CL-DATA-FRAME:DATA-FRAME (1 x 10006)
  :A 10001 reals, min=0, q25=24.9975, q50=50, q75=75.0025, max=100;
     3 (0%) x NIL, 2 (0%) x "missing">

A more realistic example with a dataset I am currently working on that has both numeric, categorical, and missing ("") data:

#<CL-DATA-FRAME:DATA-FRAME (20 x 1082)
  :IDHH 1082 reals, min=7, q25=1351, q50=2548, q75=4073, max=5434
  :IDPERS bits, ones: 1082 (100%)
  :AGE 1082 reals, min=25, q25=41.17526, q50=49.492752, q75=59.814816, max=63
  :GENDER 832 (77%) x "weiblich", 250 (23%) x "maennlich"
  :MARITAL 515 (48%) x "geschieden",
           331 (31%) x "ledig",
           153 (14%) x "verwitwet",
           83 (8%) x "dauernd getrennt lebend"
  :SCHOOL 419 (39%) x "mittlere reife, realschulabschluss",
          338 (31%) x "volksschul-/hauptschulabschluss",
          217 (20%) x "abitur (hochschulreife)",
          87 (8%) x "fachoberschule, fachabitur",
          13 (1%) x "keine angabe",
          8 (1%) x "schule ohne abschluss verlassen"
  :WTTYPN 756 (70%) x "montag bis freitag",
          172 (16%) x "samstag",
          154 (14%) x "sonntag"
  :TMW 1082 reals, min=0, q25=0, q50=4.151436, q75=105, max=740
  :HOURS_MAINJOB 1082 reals, min=0, q25=0, q50=3.0288463, q75=9.53125, max=690
  :HOURS_ADDJOB 1082 reals, min=0, q25=0, q50=1.388621, q75=17.039537, max=450
  :THP 1082 reals, min=0, q25=141.15384, q50=263.13727, q75=386.55173, max=760
  :JUKIGR 664 (61%) x "anderer wert/trifft nicht zu oder kein wert vorhanden",
          165 (15%) x "10 bis unter 15",
          104 (10%) x "6 bis unter 10",
          80 (7%) x "18 bis unter 27",
          53 (5%) x "15 bis unter 18",
          16 (1%) x "27 und älter"
  :LEISURE 1082 reals, min=70, q25=437.74194, q50=601.8919, q75=752.069, max=960
  :USUAL_HOURS 1082 reals, min=300, q25=25138.87, q50=82259.11, q75=99997.82,
               max=99999
  :HHTYPE 664 (61%) x 1, 418 (39%) x 2
  :WORK bits, ones: 285 (26%)
  :MAINWAGE 1078 reals, min=0, q25=0, q50=36.24454, q75=153.93013, max=4100;
            4 (0%) x ""
  :ADDWAGE 1063 reals, min=0, q25=0, q50=6.7724867, q75=34.89418, max=1250;
           19 (2%) x ""
  :WAGE 1059 reals, min=0, q25=0, q50=16.293531, q75=49.222637, max=4100;
        23 (2%) x ""
  :NONWAGE_INCOME 1082 reals, min=0, q25=619.7917, q50=935.9649, q75=1293.9656,
                  max=4800>

This is the first time I used CL's pretty printer, so there might be a few bugs in there. The code is in the repository, you also need to update cl-num-utils.