Perform operations on subgroups of data

agdata = {{clay, seedB, 175}, {silty, seedB, 180}, {clay, seedB, 165}, {sandy, seedA, 168}, {clay, seedA, 184}, {sandy, seedB, 171}, {sandy, seedB, 173}, {sandy, seedA, 189}, {clay, seedA, 186}, {silty, seedB, 174}, {clay, seedA, 192}, {clay, seedA, 184}, {clay, seedA, 179}, {sandy, seedA, 182}, {sandy, seedB, 177}, {silty, seedA, 180}, {clay, seedB, 175}, {silty, seedB, 181}, {sandy, seedA, 176}, {silty, seedB, 190}};

bySoilType = GatherBy[agdata, First]

{{{clay, seedB, 175}, {clay, seedB, 165}, {clay, seedA, 184}, {clay, seedA, 186}, {clay, seedA, 192}, {clay, seedA, 184}, {clay, seedA, 179}, {clay, seedB, 175}}, {{silty, seedB, 180}, {silty, seedB, 174}, {silty, seedA, 180}, {silty, seedB, 181}, {silty, seedB, 190}}, {{sandy, seedA, 168}, {sandy, seedB, 171}, {sandy, seedB, 173}, {sandy, seedA, 189}, {sandy, seedA, 182}, {sandy, seedB, 177}, {sandy, seedA, 176}}}

Table[{x[[1, 1]], N[Mean[x[[All, -1]]]]}, {x, bySoilType}]

{{clay, 180.}, {silty, 181.}, {sandy, 176.57142857142858}}

bySeedType = GatherBy[agdata, #[[2]]&]

{{{clay, seedB, 175}, {silty, seedB, 180}, {clay, seedB, 165}, {sandy, seedB, 171}, {sandy, seedB, 173}, {silty, seedB, 174}, {sandy, seedB, 177}, {clay, seedB, 175}, {silty, seedB, 181}, {silty, seedB, 190}}, {{sandy, seedA, 168}, {clay, seedA, 184}, {sandy, seedA, 189}, {clay, seedA, 186}, {clay, seedA, 192}, {clay, seedA, 184}, {clay, seedA, 179}, {sandy, seedA, 182}, {silty, seedA, 180}, {sandy, seedA, 176}}}

Table[{x[[1, 2]], N[Mean[x[[All, -1]]]]}, {x, bySeedType}]

{{seedB, 176.1}, {seedA, 182.}}

Table[{x[[1, 2]], {N[Min[x[[All, -1]]]], N[Max[x[[All, -1]]]]}}, {x, bySeedType}]

{{seedB, {165., 190.}}, {seedA, {168., 192.}}}

meddata = {{drugB, 67, 18}, {drugB, 48, 18}, {drugA, 33, 16}, {drugB, 76, 33}, {drugB, 33, 3}, {placebo, 40, 15}, {drugB, 78, 28}, {drugB, 54, 13}, {placebo, 46, 23}, {drugA, 36, 12}, {drugA, 69, 30}, {drugA, 78, 40}, {placebo, 77, 37}, {drugA, 79, 36}, {drugA, 45, 16}, {drugA, 36, 18}, {drugA, 58, 24}, {placebo, 25, 9}, {drugB, 75, 25}, {drugB, 22, 3}, {placebo, 51, 25}, {placebo, 27, 8}, {placebo, 47, 20}, {placebo, 69, 34}, {drugB, 52, 16}};

byDrug = GatherBy[meddata, First]

{{{drugB, 67, 18}, {drugB, 48, 18}, {drugB, 76, 33}, {drugB, 33, 3}, {drugB, 78, 28}, {drugB, 54, 13}, {drugB, 75, 25}, {drugB, 22, 3}, {drugB, 52, 16}}, {{drugA, 33, 16}, {drugA, 36, 12}, {drugA, 69, 30}, {drugA, 78, 40}, {drugA, 79, 36}, {drugA, 45, 16}, {drugA, 36, 18}, {drugA, 58, 24}}, {{placebo, 40, 15}, {placebo, 46, 23}, {placebo, 77, 37}, {placebo, 25, 9}, {placebo, 51, 25}, {placebo, 27, 8}, {placebo, 47, 20}, {placebo, 69, 34}}}

describe[values_] := {Length[values], Mean[values], Median[values], {Min[values], Max[values]}}

Table[{x[[1, 1]], describe[N[x[[All, -1]]]]}, {x, byDrug} ]

{{drugB, {9, 17.444444444444443, 18., {3., 33.}}}, {drugA, {8, 24., 21., {12., 40.}}}, {placebo, {8, 21.375, 21.5, {8., 37.}}}}

byAgeGroup = GatherBy[meddata, IntegerPart[#[[2]] / 10]&]

{{{drugB, 67, 18}, {drugA, 69, 30}, {placebo, 69, 34}}, {{drugB, 48, 18}, {placebo, 40, 15}, {placebo, 46, 23}, {drugA, 45, 16}, {placebo, 47, 20}}, {{drugA, 33, 16}, {drugB, 33, 3}, {drugA, 36, 12}, {drugA, 36, 18}}, {{drugB, 76, 33}, {drugB, 78, 28}, {drugA, 78, 40}, {placebo, 77, 37}, {drugA, 79, 36}, {drugB, 75, 25}}, {{drugB, 54, 13}, {drugA, 58, 24}, {placebo, 51, 25}, {drugB, 52, 16}}, {{placebo, 25, 9}, {drugB, 22, 3}, {placebo, 27, 8}}}

Table[{10IntegerPart[x[[1, 2]] / 10], describe[N[x[[All, -1]]]]}, {x, byAgeGroup}]//Sort

{{20, {3, 6.666666666666667, 8., {3., 9.}}}, {30, {4, 12.25, 14., {3., 18.}}}, {40, {5, 18.4, 18., {15., 23.}}}, {50, {4, 19.5, 20., {13., 25.}}}, {60, {3, 27.333333333333332, 30., {18., 34.}}}, {70, {6, 33.166666666666664, 34.5, {25., 40.}}}}

byDrugAndAgeGroup = GatherBy[meddata, {First[#], IntegerPart[#[[2]] / 10]}&]

{{{drugB, 67, 18}}, {{drugB, 48, 18}}, {{drugA, 33, 16}, {drugA, 36, 12}, {drugA, 36, 18}}, {{drugB, 76, 33}, {drugB, 78, 28}, {drugB, 75, 25}}, {{drugB, 33, 3}}, {{placebo, 40, 15}, {placebo, 46, 23}, {placebo, 47, 20}}, {{drugB, 54, 13}, {drugB, 52, 16}}, {{drugA, 69, 30}}, {{drugA, 78, 40}, {drugA, 79, 36}}, {{placebo, 77, 37}}, {{drugA, 45, 16}}, {{drugA, 58, 24}}, {{placebo, 25, 9}, {placebo, 27, 8}}, {{drugB, 22, 3}}, {{placebo, 51, 25}}, {{placebo, 69, 34}}}

Table[{x[[1, 1]], 10IntegerPart[x[[1, 2]] / 10], describe[N[x[[All, -1]]]]}, {x, byDrugAndAgeGroup}]//Sort//Grid

Grid[{{drugA, 30, {3, 15.333333333333334, 16., {12., 18.}}}, {drugA, 40, {1, 16., 16., {16., 16.}}}, {drugA, 50, {1, 24., 24., {24., 24.}}}, {drugA, 60, {1, 30., 30., {30., 30.}}}, {drugA, 70, {2, 38., 38., {36., 40.}}}, {drugB, 20, {1, 3., 3., {3., 3.}}}, {drugB, 30, {1, 3., 3., {3., 3.}}}, {drugB, 40, {1, 18., 18., {18., 18.}}}, {drugB, 50, {2, 14.5, 14.5, {13., 16.}}}, {drugB, 60, {1, 18., 18., {18., 18.}}}, {drugB, 70, {3, 28.666666666666668, 28., {25., 33.}}}, {placebo, 20, {2, 8.5, 8.5, {8., 9.}}}, {placebo, 40, {3, 19.333333333333332, 20., {15., 23.}}}, {placebo, 50, {1, 25., 25., {25., 25.}}}, {placebo, 60, {1, 34., 34., {34., 34.}}}, {placebo, 70, {1, 37., 37., {37., 37.}}}}]