R remove named list() dead ends from nested list

Question

I have a nested list;

my_list <- list(ACESAC = list(predictor_2_list = list(ACESAC_spectral_predictors_2 = list(
    `NDVI_10;MCARI_MTVI` = structure(list(spectral_2 = 0.507, 
        species = "ACESAC"), class = "data.frame", row.names = c(NA, 
    -1L))))), ARANUD = list(predictor_2_list = list(ARANUD_spectral_predictors_2 = structure(list(), .Names = character(0)))))

my_list$ARANUD$predictor_2_list$ARANUD_spectral_predictors_2 is ultimately empty, though. It returns named list(), but has no contents.

Given that my_list$ARANUD is ultimately a dead-end, I would like to remove it.

The desired result would look like;

my_list_reduced <- list(ACESAC = list(predictor_2_list = list(ACESAC_spectral_predictors_2 = list(
    `NDVI_10;MCARI_MTVI` = structure(list(spectral_2 = 0.507, 
        species = "ACESAC"), class = "data.frame", row.names = c(NA, 
    -1L))))))

The ideal solution would be able to be applied using any level of nesting and would cut the list back to the point where a dead end begins.

Therefore, given my_list2, no named list() dead ends would be present but no actual data would be lost.

my_list2 <- list(ABIBAL = list(predictor_1_list = list(ABIBAL_all_predictors_1 = structure(list(), .Names = character(0)), 
    ABIBAL_topo_predictors_1 = structure(list(), .Names = character(0)), 
    ABIBAL_spectral_predictors_1 = structure(list(), .Names = character(0)), 
    ABIBAL_topo_spectral_predictors_1 = structure(list(), .Names = character(0)), 
    ABIBAL_soils_predictors_1 = structure(list(), .Names = character(0))), 
    predictor_2_list = list(ABIBAL_all_predictors_2 = list(`B.Al;NDVI_10` = 0.656), 
        ABIBAL_topo_predictors_2 = list(`tpi25.MEAN;twi_dd.STD` = 0.644), 
        ABIBAL_spectral_predictors_2 = list(`NDVI_10;MCARI_MTVI` = 0.649), 
        ABIBAL_topo_spectral_predictors_2 = list(`TAS_mean.MEAN;solar_rad_total_20m` = 0.675), 
        ABIBAL_soils_predictors_2 = list(`B.Al;OA.pH` = 0.718)), 
    predictor_3_list = list(ABIBAL_all_predictors_3 = list(`B.Al;OA.P;NDVI_10` = 0.805), 
        ABIBAL_topo_predictors_3 = list(`TAS_mean.MEAN;tpi25.MEAN;solar_rad_total_20m` = 0.707), 
        ABIBAL_spectral_predictors_3 = list(`NDWI_10;NDVI_10;MCARI_MTVI` = 0.558), 
        ABIBAL_topo_spectral_predictors_3 = list(`TAS_mean.MEAN;solar_rad_total_20m;NDWI_10` = 0.729), 
        ABIBAL_soils_predictors_3 = list(`OA.Al;OA.pH;B.C` = 0.758))))

This question is similar to Remove NULL elements from list of lists but I do not have list elements that are NULL. Instead, my lists dead end in named list() that is empty.

So for your `my_list2` you want `predictor_1_list` present? – starja Sep 25 '20 at 19:10 — starja, Sep 25 '20 at 19:10

score 1 · Accepted Answer · answered Sep 25 '20 at 19:42

Using rrapply in the rrapply-package it suffices to set how = "prune" to prune all empty list components:

rrapply::rrapply(my_list, how = "prune")

#> $ACESAC
#> $ACESAC$predictor_2_list
#> $ACESAC$predictor_2_list$ACESAC_spectral_predictors_2
#> $ACESAC$predictor_2_list$ACESAC_spectral_predictors_2$`NDVI_10;MCARI_MTVI`
#>   spectral_2 species
#> 1      0.507  ACESAC

For my_list2 the complete predictor_1_list component is pruned as it consists of only empty lists:

str(rrapply::rrapply(my_list2, how = "prune"))

#> List of 1
#>  $ ABIBAL:List of 2
#>   ..$ predictor_2_list:List of 5
#>   .. ..$ ABIBAL_all_predictors_2          :List of 1
#>   .. .. ..$ B.Al;NDVI_10: num 0.656
#>   .. ..$ ABIBAL_topo_predictors_2         :List of 1
#>   .. .. ..$ tpi25.MEAN;twi_dd.STD: num 0.644
#>   .. ..$ ABIBAL_spectral_predictors_2     :List of 1
#>   .. .. ..$ NDVI_10;MCARI_MTVI: num 0.649
#>   .. ..$ ABIBAL_topo_spectral_predictors_2:List of 1
#>   .. .. ..$ TAS_mean.MEAN;solar_rad_total_20m: num 0.675
#>   .. ..$ ABIBAL_soils_predictors_2        :List of 1
#>   .. .. ..$ B.Al;OA.pH: num 0.718
#>   ..$ predictor_3_list:List of 5
#>   .. ..$ ABIBAL_all_predictors_3          :List of 1
#>   .. .. ..$ B.Al;OA.P;NDVI_10: num 0.805
#>   .. ..$ ABIBAL_topo_predictors_3         :List of 1
#>   .. .. ..$ TAS_mean.MEAN;tpi25.MEAN;solar_rad_total_20m: num 0.707
#>   .. ..$ ABIBAL_spectral_predictors_3     :List of 1
#>   .. .. ..$ NDWI_10;NDVI_10;MCARI_MTVI: num 0.558
#>   .. ..$ ABIBAL_topo_spectral_predictors_3:List of 1
#>   .. .. ..$ TAS_mean.MEAN;solar_rad_total_20m;NDWI_10: num 0.729
#>   .. ..$ ABIBAL_soils_predictors_3        :List of 1
#>   .. .. ..$ OA.Al;OA.pH;B.C: num 0.758

R remove named list() dead ends from nested list

1 Answers1