python - conditional selection on pandas dataframe

Question

I have dataset in given form

   time    color height weight value
1  t1      red    hr1     wr1     vr1
2  t1      red    hr1     wr1     vr1
3  t1      blue   hb1     wb1    vb1
4  t1      blue   hb1     wb1     vb1
5  t1      green  hg1     wg1     vg1
6  t1      green  hg1     wg1     vg1
7  t2      blue   hb2     wb2     vb2
8  t2      green  hg2     wg2    vg2
9  t2      red    hr2     wr2     vr2
10 t2      red    hr2     wr2     vr2
11 t3      red    hr3     wr3     vr3
12 t3      red    hr3     wr3     vr3
13 t3      green  hg3     wg3     vg3
14 t3      green  hg3     wg3     vg3
15 t3      blue   hb3     wb3     vb3
16 t3      blue   hb3     wb3     vb3

I would like to drop the measurements of time where the color do not have same count value of 2 for each red, blue green. In the given snippet, t1 and t3 should be retained and all rows for t3 measurements should be dropped.

The result should be:

 time   color height weight value
1  t1      red    hr1     wr1     vr1
2  t1      red    hr1     wr1     vr1
3  t1      blue   hb1     wb1    vb1
4  t1      blue   hb1     wb1     vb1
5  t1      green  hg1     wg1     vg1
6  t1      green  hg1     wg1     vg1
7  t3      red    hr3     wr3     vr3
8  t3      red    hr3     wr3     vr3
9  t3      green  hg3     wg3     vg3
10 t3      green  hg3     wg3     vg3
11  t3     blue   hb3     wb3     vb3
12  t3     blue   hb3     wb3     vb3

Thank you,

标签： pythonpandas

Answer 1

怎么样：

s = df.groupby(['time', 'color']).size()
s = s.unstack(0).eq(2).all()
valid_times = s.index[s]

print(df[df.time.isin(valid_times)])

   time  color height weight value
1    t1    red    hr1    wr1   vr1
2    t1    red    hr1    wr1   vr1
3    t1   blue    hb1    wb1   vb1
4    t1   blue    hb1    wb1   vb1
5    t1  green    hg1    wg1   vg1
6    t1  green    hg1    wg1   vg1
11   t3    red    hr3    wr3   vr3
12   t3    red    hr3    wr3   vr3
13   t3  green    hg3    wg3   vg3
14   t3  green    hg3    wg3   vg3
15   t3   blue    hb3    wb3   vb3
16   t3   blue    hb3    wb3   vb3